N-2 - $ / shares	3 Months Ended
N-2 - $ / shares	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2024	Mar. 31, 2024
Cover [Abstract]
Entity Central Index Key	0001321741
Amendment Flag	false
Securities Act File Number	814-00704
Document Type	10-Q
Entity Registrant Name	GLADSTONE INVESTMENT CORPORATION\DE
Entity Address, Address Line One	1521 WESTBRANCH DRIVE
Entity Address, Address Line Two	SUITE 100
Entity Address, City or Town	MCLEAN
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	22102
City Area Code	703
Local Phone Number	287-5800
Entity Emerging Growth Company	false
Financial Highlights [Abstract]
Senior Securities, Note [Text Block]	As of June 30, 2025, our asset coverage ratio on our senior securities representing indebtedness was 189.8%.
General Description of Registrant [Abstract]
Investment Objectives and Practices [Text Block]	We were established for the purpose of investing in debt and equity securities of established private businesses operating in the United States (“U.S.”). Our investment objectives are to: (i) achieve and grow current income by investing in debt securities of established businesses that we believe will provide stable earnings and cash flow to pay expenses, make principal and interest payments on our outstanding indebtedness, and make distributions to our stockholders that grow over time; and (ii) provide our stockholders with long-term capital appreciation in the value of our assets by investing in equity securities of established businesses, generally in combination with the aforementioned debt securities, that we believe can grow over time to permit us to sell our equity investments for capital gains. To achieve our objectives, our investment strategy is to invest in several categories of debt and equity securities, with individual investments generally totaling up to $75 million, although investment size may vary depending upon our total assets or available capital at the time of investment. We expect that our investment portfolio over time will consist of approximately 75% in debt investments and 25% in equity investments, at cost. We focus on investing in lower middle market private businesses (which we generally define as companies with annual earnings before interest, taxes, depreciation and amortization (“EBITDA”) of $4 million to $15 million) (“Lower Middle Market”) in the U.S. that meet certain criteria, including: the sustainability of the business’ free cash flow and its ability to grow it over time, adequate assets for loan collateral, experienced management teams with a significant ownership interest in the portfolio company, reasonable capitalization of the portfolio company, including an ample equity contribution or cushion based on prevailing enterprise valuation multiples, and the potential to realize appreciation and gain liquidity in our equity position, if any. We anticipate that liquidity in our equity position will be achieved through a merger, acquisition or recapitalization of the portfolio company, a public offering of the portfolio company’s stock, or, to a lesser extent, by exercising our right to require the portfolio company to repurchase our warrants, though there can be no assurance that we will always have these rights. We invest in portfolio companies that seek funds for management buyouts and/or growth capital to finance acquisitions, recapitalize or, to a lesser extent, refinance their existing debt facilities. We seek to avoid investing in high-risk, early-stage enterprises. Our targeted portfolio companies are generally considered too small for the larger capital marketplace.
Risk [Text Block]	ITEM 1A. RISK FACTORS. Our business is subject to certain risks and events that, if they occur, could adversely affect our financial condition and results of operations and the trading price of our securities. For a discussion of these risks, please refer to the section captioned “Item 1A. Risk Factors” in Part I of our Annual Report on Form 10-K for the fiscal year ended March 31, 2025, as filed with the SEC on May 13, 2025. The risks described in our Annual Report are not the only risks we face. Additional risks and uncertainties not currently known to us or that we currently deem to be immaterial also may materially and adversely affect our business, financial condition and/or operating results.
Share Price	$ 14.27
NAV Per Share	$ 12.99	$ 13.55	$ 13.01	$ 13.43
Latest Premium (Discount) to NAV [Percent]	9.90%
Capital Stock, Long-Term Debt, and Other Securities [Abstract]
Long Term Debt [Table Text Block]	Notes Payable
Revolving Line Of Credit [Member]
Capital Stock, Long-Term Debt, and Other Securities [Abstract]
Long Term Debt [Table Text Block]	Revolving Line of Credit As of June 30, 2025, our Credit Facility had a total commitment amount of $270.0 million with an "accordion" feature that permits us to increase the size of the facility to $300.0 million. The Credit Facility has a revolving period end date of October 30, 2026 and a final maturity date of October 30, 2028 (at which time all principal and interest will be due and payable if the Credit Facility is not extended by the revolving period end date) As of June 30, 2025, advances under the Credit Facility generally bore interest at 30-day Term SOFR, subject to a floor of 0.35%, with a SOFR credit spread adjustment of 10 basis points, plus a margin of 3.15% per annum until October 30, 2026, with the margin then increasing to 3.40% for the period from October 30, 2026 to October 30, 2027, and increasing further to 3.65% thereafter. The Credit Facility has an unused commitment fee on the daily unused commitment amount of 0.50% per annum if the daily unused commitment amount is less than or equal to 50% of the total commitment amount, 0.75% per annum if the daily unused commitment amount is greater than 50% but less than or equal to 65% of the total commitment amount, and 1.00% per annum if the daily unused commitment amount is greater than 65% of the total commitment amount. At June 30, 2025, we had $62.0 million of borrowings outstanding on the Credit Facility and as of the date of this report, we had $119.2 million outstanding under our Credit Facility. Interest is payable monthly during the term of our Credit Facility. Available borrowings are subject to various constraints and applicable advance rates, which are generally based on the size, characteristics, and quality of the collateral pledged by Business Investment. Our Credit Facility also requires that any interest and principal payments on pledged loans be remitted directly by the borrower into a lockbox account with KeyBank. KeyBank is also the trustee of the account and generally remits the collected funds to us once a month. Among other things, our Credit Facility contains covenants that require Business Investment to maintain its status as a separate legal entity, prohibit certain significant corporate transactions (such as mergers, consolidations, liquidations or dissolutions) and restrict certain material changes to our credit and collection policies without the lenders’ consent. Our Credit Facility also generally seeks to restrict distributions to stockholders to the sum of (i) our net investment income, (ii) net capital gains, and (iii) amounts deemed by the Company to be considered as having been paid during the prior fiscal year in accordance with Section 855(a) of the Code. Loans eligible to be pledged as collateral are subject to certain limitations, including, among other things, restrictions on geographic concentrations, industry concentrations, loan size, payment frequency and status, average life, portfolio company leverage, and lien property. Our Credit Facility also requires Business Investment to comply with other financial and operational covenants, which obligate Business Investment to, among other things, maintain certain financial ratios, including asset and interest coverage and a minimum number of obligors required in the borrowing base. Additionally, our Credit Facility contains a performance guaranty that requires the Company to maintain (i) a minimum net worth of the greater of $210.0 million or $210.0 million plus 50% of all equity and subordinated debt raised, minus 50% of any equity or subordinated debt redeemed or retired after November 16, 2016, which equated to $416.6 million as of June 30, 2025, (ii) asset coverage with respect to senior securities representing indebtedness of at least 150% (or such percentage as may be set forth in Section 18 of the 1940 Act, as modified by Section 61 of the 1940 Act), and (iii) our status as a BDC under the 1940 Act and as a RIC under the Code. As of June 30, 2025, and as defined in the performance guaranty of our Credit Facility, we had a net worth of $940.4 million, asset coverage on our senior securities representing indebtedness of 189.8%, calculated in compliance with the requirements of Sections 18 and 61 of the 1940 Act, and an active status as a BDC and RIC. As of June 30, 2025, we had availability, after adjustments for various constraints based on collateral quality, of $208.0 million under our Credit Facility and were in compliance with all covenants under our Credit Facility.
Long Term Debt, Structuring [Text Block]	Revolving Line of Credit As of June 30, 2025, our Credit Facility had a total commitment amount of $270.0 million with an "accordion" feature that permits us to increase the size of the facility to $300.0 million. The Credit Facility has a revolving period end date of October 30, 2026 and a final maturity date of October 30, 2028 (at which time all principal and interest will be due and payable if the Credit Facility is not extended by the revolving period end date)
5.00% Notes Due 2026 [Member]
Capital Stock, Long-Term Debt, and Other Securities [Abstract]
Long Term Debt [Table Text Block]	5.00% Notes due 2026 In March 2021, we completed a public offering of the 5.00% 2026 Notes with an aggregate principal amount of $127.9 million, which resulted in net proceeds of approximately $123.8 million after deducting underwriting discounts, commissions and offering costs borne by us. The 5.00% 2026 Notes are traded under the ticker symbol “GAINN” on Nasdaq. The 5.00% 2026 Notes will mature on May 1, 2026 and may be redeemed in whole or in part at any time or from time to time at the Company’s option. The 5.00% 2026 Notes bear interest at a rate of 5.00% per year (which equates to $6.4 million per year), payable quarterly in arrears. The indenture relating to the 5.00% 2026 Notes contains certain covenants, including (i) an inability to incur additional debt or issue additional debt or preferred securities unless the Company’s asset coverage meets the threshold specified in the 1940 Act after such borrowing, (ii) an inability to declare any dividend or distribution (except a dividend payable in our stock) on a class of our capital stock or to purchase shares of our capital stock unless the Company’s asset coverage meets the threshold specified in the 1940 Act at the time of (and giving effect to) such declaration or purchase, and (iii) if, at any time, we are not subject to the reporting requirements of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), we will provide the holders of the 5.00% 2026 Notes and the trustee with audited annual consolidated financial statements and unaudited interim consolidated financial statements. The 5.00% 2026 Notes are recorded at the aggregate principal amount, less underwriting discounts, commissions, and offering costs, on our accompanying Consolidated Statements of Assets and Liabilities. Total underwriting discounts, commissions, and offering costs related to this offering were $4.1 million, which have been recorded as discounts to the aggregate principal amount on our accompanying Consolidated Statements of Assets and Liabilities and are being amortized over the period ending May 1, 2026, the maturity date.
Long Term Debt, Title [Text Block]	5.00% Notes due 2026
Long Term Debt, Structuring [Text Block]	In March 2021, we completed a public offering of the 5.00% 2026 Notes with an aggregate principal amount of $127.9 million, which resulted in net proceeds of approximately $123.8 million after deducting underwriting discounts, commissions and offering costs borne by us. The 5.00% 2026 Notes are traded under the ticker symbol “GAINN” on Nasdaq. The 5.00% 2026 Notes will mature on May 1, 2026 and may be redeemed in whole or in part at any time or from time to time at the Company’s option. The 5.00% 2026 Notes bear interest at a rate of 5.00% per year (which equates to $6.4 million per year), payable quarterly in arrears.
Long Term Debt, Dividends and Covenants [Text Block]	The indenture relating to the 5.00% 2026 Notes contains certain covenants, including (i) an inability to incur additional debt or issue additional debt or preferred securities unless the Company’s asset coverage meets the threshold specified in the 1940 Act after such borrowing, (ii) an inability to declare any dividend or distribution (except a dividend payable in our stock) on a class of our capital stock or to purchase shares of our capital stock unless the Company’s asset coverage meets the threshold specified in the 1940 Act at the time of (and giving effect to) such declaration or purchase, and (iii) if, at any time, we are not subject to the reporting requirements of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), we will provide the holders of the 5.00% 2026 Notes and the trustee with audited annual consolidated financial statements and unaudited interim consolidated financial statements.
4.875% Notes Due 2028 [Member]
Capital Stock, Long-Term Debt, and Other Securities [Abstract]
Long Term Debt [Table Text Block]	4.875% Notes due 2028 In August 2021, we completed a public offering of the 4.875% 2028 Notes with an aggregate principal amount of $134.6 million, which resulted in net proceeds of approximately $131.3 million after deducting underwriting discounts, commissions and offering costs borne by us. The 4.875% 2028 Notes are traded under the ticker symbol “GAINZ” on Nasdaq. The 4.875% 2028 Notes will mature on November 1, 2028 and may be redeemed in whole or in part at any time or from time to time at the Company’s option. The 4.875% 2028 Notes bear interest at a rate of 4.875% per year (which equates to $6.6 million per year), payable quarterly in arrears. The indenture relating to the 4.875% 2028 Notes contains certain covenants, including (i) an inability to incur additional debt or issue additional debt or preferred securities unless the Company’s asset coverage meets the threshold specified in the 1940 Act after such borrowing, (ii) an inability to declare any dividend or distribution (except a dividend payable in our stock) on a class of our capital stock or to purchase shares of our capital stock unless the Company’s asset coverage meets the threshold specified in the 1940 Act at the time of (and giving effect to) such declaration or purchase, and (iii) if, at any time, we are not subject to the reporting requirements of the Exchange Act, we will provide the holders of the 4.875% 2028 Notes and the trustee with audited annual consolidated financial statements and unaudited interim consolidated financial statements. The 4.875% 2028 Notes are recorded at the aggregate principal amount, less underwriting discounts, commissions, and offering costs, on our accompanying Consolidated Statements of Assets and Liabilities. Total underwriting discounts, commissions, and offering costs related to this offering were $3.3 million, which have been recorded as discounts to the aggregate principal amount on our accompanying Consolidated Statements of Assets and Liabilities and are being amortized over the period ending November 1, 2028, the maturity date.
Long Term Debt, Title [Text Block]	4.875% Notes due 2028
Long Term Debt, Structuring [Text Block]	In August 2021, we completed a public offering of the 4.875% 2028 Notes with an aggregate principal amount of $134.6 million, which resulted in net proceeds of approximately $131.3 million after deducting underwriting discounts, commissions and offering costs borne by us. The 4.875% 2028 Notes are traded under the ticker symbol “GAINZ” on Nasdaq. The 4.875% 2028 Notes will mature on November 1, 2028 and may be redeemed in whole or in part at any time or from time to time at the Company’s option. The 4.875% 2028 Notes bear interest at a rate of 4.875% per year (which equates to $6.6 million per year), payable quarterly in arrears.
Long Term Debt, Dividends and Covenants [Text Block]	The indenture relating to the 4.875% 2028 Notes contains certain covenants, including (i) an inability to incur additional debt or issue additional debt or preferred securities unless the Company’s asset coverage meets the threshold specified in the 1940 Act after such borrowing, (ii) an inability to declare any dividend or distribution (except a dividend payable in our stock) on a class of our capital stock or to purchase shares of our capital stock unless the Company’s asset coverage meets the threshold specified in the 1940 Act at the time of (and giving effect to) such declaration or purchase, and (iii) if, at any time, we are not subject to the reporting requirements of the Exchange Act, we will provide the holders of the 4.875% 2028 Notes and the trustee with audited annual consolidated financial statements and unaudited interim consolidated financial statements.
8.00% Notes Due 2028 [Member]
Capital Stock, Long-Term Debt, and Other Securities [Abstract]
Long Term Debt [Table Text Block]	8.00% Notes due 2028 In May 2023, we completed a public offering of the 8.00% 2028 Notes with an aggregate principal amount of $74.8 million, which resulted in net proceeds of approximately $72.3 million after deducting underwriting discounts, commissions and offering costs borne by us. The 8.00% 2028 Notes are traded under the ticker symbol “GAINL” on Nasdaq. The 8.00% 2028 Notes will mature on August 1, 2028 and may be redeemed in whole or in part at any time or from time to time at the Company’s option. The 8.00% 2028 Notes bear interest at a rate of 8.00% per year (which equates to $6.0 million per year), payable quarterly in arrears. The indenture relating to the 8.00% 2028 Notes contains certain covenants, including (i) an inability to incur additional debt or issue additional debt or preferred securities unless the Company’s asset coverage meets the threshold specified in the 1940 Act after such borrowing, (ii) an inability to declare any dividend or distribution (except a dividend payable in our stock) on a class of our capital stock or to purchase shares of our capital stock unless the Company’s asset coverage meets the threshold specified in the 1940 Act at the time of (and giving effect to) such declaration or purchase, and (iii) if, at any time, we are not subject to the reporting requirements of the Exchange Act, we will provide the holders of the 8.00% 2028 Notes and the trustee with audited annual consolidated financial statements and unaudited interim consolidated financial statements. The 8.00% 2028 Notes are recorded at the aggregate principal amount, less underwriting discounts, commissions, and offering costs, on our accompanying Consolidated Statements of Assets and Liabilities. Total underwriting discounts, commissions, and offering costs related to this offering were $2.5 million, which have been recorded as discounts to the aggregate principal amount on our accompanying Consolidated Statements of Assets and Liabilities and are being amortized over the period ending August 1, 2028, the maturity date.
Long Term Debt, Title [Text Block]	8.00% Notes due 2028
Long Term Debt, Structuring [Text Block]	In May 2023, we completed a public offering of the 8.00% 2028 Notes with an aggregate principal amount of $74.8 million, which resulted in net proceeds of approximately $72.3 million after deducting underwriting discounts, commissions and offering costs borne by us. The 8.00% 2028 Notes are traded under the ticker symbol “GAINL” on Nasdaq. The 8.00% 2028 Notes will mature on August 1, 2028 and may be redeemed in whole or in part at any time or from time to time at the Company’s option. The 8.00% 2028 Notes bear interest at a rate of 8.00% per year (which equates to $6.0 million per year), payable quarterly in arrears.
Long Term Debt, Dividends and Covenants [Text Block]	The indenture relating to the 8.00% 2028 Notes contains certain covenants, including (i) an inability to incur additional debt or issue additional debt or preferred securities unless the Company’s asset coverage meets the threshold specified in the 1940 Act after such borrowing, (ii) an inability to declare any dividend or distribution (except a dividend payable in our stock) on a class of our capital stock or to purchase shares of our capital stock unless the Company’s asset coverage meets the threshold specified in the 1940 Act at the time of (and giving effect to) such declaration or purchase, and (iii) if, at any time, we are not subject to the reporting requirements of the Exchange Act, we will provide the holders of the 8.00% 2028 Notes and the trustee with audited annual consolidated financial statements and unaudited interim consolidated financial statements.
7.875% Notes Due 2030 [Member]
Capital Stock, Long-Term Debt, and Other Securities [Abstract]
Long Term Debt [Table Text Block]	7.875% Notes due 2030 In December 2024, we completed a public offering of the 7.875% 2030 Notes with an aggregate principal amount of $126.5 million, which resulted in net proceeds of approximately $122.4 million after deducting underwriting discounts, commissions and offering costs borne by us. The 7.875% 2030 Notes are traded under the ticker symbol “GAINI” on Nasdaq. The 7.875% 2030 Notes will mature on February 1, 2030 and may be redeemed in whole or in part at any time or from time to time at the Company’s option on or after February 1, 2027. The 7.875% 2030 Notes bear interest at a rate of 7.875% per year (which equates to $10.0 million per year), payable quarterly in arrears. The indenture relating to the 7.875% 2030 Notes contains certain covenants, including (i) an inability to incur additional debt or issue additional debt or preferred securities unless the Company’s asset coverage meets the threshold specified in the 1940 Act after such borrowing, (ii) an inability to declare any dividend or distribution (except a dividend payable in our stock) on a class of our capital stock or to purchase shares of our capital stock unless the Company’s asset coverage meets the threshold specified in the 1940 Act at the time of (and giving effect to) such declaration or purchase, and (iii) if, at any time, we are not subject to the reporting requirements of the Exchange Act, we will provide the holders of the 7.875% 2030 Notes and the trustee with audited annual consolidated financial statements and unaudited interim consolidated financial statements. The 7.875% 2030 Notes are recorded at the aggregate principal amount, less underwriting discounts, commissions, and offering costs, on our accompanying Consolidated Statements of Assets and Liabilities. Total underwriting discounts, commissions, and offering costs related to this offering were $4.1 million, which have been recorded as discounts to the aggregate principal amount on our accompanying Consolidated Statements of Assets and Liabilities and are being amortized over the period ending February 1, 2030, the maturity date.
Long Term Debt, Title [Text Block]	7.875% Notes due 2030
Long Term Debt, Structuring [Text Block]	In December 2024, we completed a public offering of the 7.875% 2030 Notes with an aggregate principal amount of $126.5 million, which resulted in net proceeds of approximately $122.4 million after deducting underwriting discounts, commissions and offering costs borne by us. The 7.875% 2030 Notes are traded under the ticker symbol “GAINI” on Nasdaq. The 7.875% 2030 Notes will mature on February 1, 2030 and may be redeemed in whole or in part at any time or from time to time at the Company’s option on or after February 1, 2027. The 7.875% 2030 Notes bear interest at a rate of 7.875% per year (which equates to $10.0 million per year), payable quarterly in arrears.
Long Term Debt, Dividends and Covenants [Text Block]	The indenture relating to the 7.875% 2030 Notes contains certain covenants, including (i) an inability to incur additional debt or issue additional debt or preferred securities unless the Company’s asset coverage meets the threshold specified in the 1940 Act after such borrowing, (ii) an inability to declare any dividend or distribution (except a dividend payable in our stock) on a class of our capital stock or to purchase shares of our capital stock unless the Company’s asset coverage meets the threshold specified in the 1940 Act at the time of (and giving effect to) such declaration or purchase, and (iii) if, at any time, we are not subject to the reporting requirements of the Exchange Act, we will provide the holders of the 7.875% 2030 Notes and the trustee with audited annual consolidated financial statements and unaudited interim consolidated financial statements.

GLADSTONE INVESTMENT CORPORATION\DE 10-Q