Debt - Narrative (Details)			6 Months Ended	12 Months Ended
Debt - Narrative (Details)	Jun. 18, 2024	Feb. 02, 2022 USD ($)	Jun. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)	Jun. 27, 2025 USD ($)	May 30, 2025 USD ($)	May 29, 2025 USD ($)	Apr. 24, 2025 USD ($)	Mar. 28, 2025 USD ($)	Mar. 20, 2025 USD ($)	Mar. 19, 2025 USD ($)	Dec. 20, 2024 USD ($)	Dec. 19, 2024 USD ($)	Dec. 12, 2024 USD ($)	Dec. 11, 2024 USD ($)	Sep. 20, 2024 USD ($)	Sep. 19, 2024 USD ($)	Sep. 16, 2024 USD ($)	Jun. 30, 2024 USD ($)	Jun. 14, 2024 USD ($)	May 01, 2024 repurchaseAgreement	Mar. 15, 2024 USD ($)	Sep. 15, 2023 USD ($)	Apr. 30, 2021	Mar. 31, 2021
Line of Credit Facility [Line Items]
Asset coverage ratio thresholds			150.00%																					150.00%	200.00%
Asset coverage ratio of 150% borrowing increase amount			$ 200
Asset coverage ratio of 200% borrowing increase amount			$ 100
Debt instrument, asset coverage ratio			242.70%	269.20%
Total debt outstanding			$ 484,482,000																$ 177,855,000
Number of collateralized repurchase agreements entered into \| repurchaseAgreement																					2
SBA-Guaranteed Debentures
Line of Credit Facility [Line Items]
Maximum borrowing capacity			350,000,000
Repurchase Obligation
Line of Credit Facility [Line Items]
Total debt outstanding			$ 0.0	$ 0.0
Reverse repurchase agreement, maximum period for repurchase			90 days
Revolver \| Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 505,000,000	417,505,000
Total debt outstanding			484,482,000	400,737,000
Revolver \| Line of Credit \| Lafayette Square \| LS SBIC LP
Line of Credit Facility [Line Items]
Committed capital			115,000,000
Revolver \| Line of Credit \| Lafayette Square \| LS SSBIC LP
Line of Credit Facility [Line Items]
Committed capital				110,000,000
Revolver \| ING Credit Facility \| Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity						$ 275,000,000	$ 250,000,000	$ 275,000,000		$ 250,000,000	$ 225,000,000	$ 225,000,000	$ 175,000,000	$ 175,000,000	$ 150,000,000	$ 150,000,000	$ 75,000,000
Maximum borrowing capacity and accordion feature increase limit								300,000,000
Repurchase agreements financing permitted								$ 30,000,000
Total debt outstanding			254,500,000	208,200,000
Revolver \| ING Credit Facility \| Line of Credit \| Secured Overnight Financing Rate (SOFR)
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.70%
Revolver \| ING Credit Facility \| Line of Credit \| Margin Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.70%
Revolver \| Subscription Facility \| Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 38,400,000
Total debt outstanding			0.0	0.0
Revolver \| Subscription Facility \| Line of Credit \| Maximum
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 1,000,000,000
Revolver \| Subscription Facility \| Line of Credit \| Margin Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate		2.50%
Revolver \| Subscription Facility \| Line of Credit \| Federal Fund Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.50%
Revolver \| SBA-Guaranteed Debentures \| Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity			230,000,000	192,505,000
Total debt outstanding			$ 230,000,000	192,505,000
Revolver \| SBA-Guaranteed Debentures \| Line of Credit \| LS SBIC LP and LS SSBIC LP
Line of Credit Facility [Line Items]
Maximum borrowing capacity					$ 27,500,000				$ 9,995,000					$ 27,500,000				$ 82,505,000		$ 45,540,000		$ 5,960,000	$ 31,000,000
Debt instrument, term			10 years
Commitment fee percentage			1.00%
Discount percentage			2.435%
Revolver \| SBA-Guaranteed Debentures \| Line of Credit \| LS SBIC LP
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 175,000,000
Revolver \| SBA-Guaranteed Debentures \| Line of Credit \| LS SSBIC LP
Line of Credit Facility [Line Items]
Maximum borrowing capacity			175,000,000
Revolver \| SBA-Guaranteed Debentures \| Line of Credit \| Lafayette Square \| LS SBIC LP
Line of Credit Facility [Line Items]
Committed capital			$ 230,000,000.0
Revolver \| SBA-Guaranteed Debentures \| Line of Credit \| Lafayette Square \| LS SSBIC LP
Line of Credit Facility [Line Items]
Committed capital				$ 192,500,000

Lafayette Square USA, Inc. 10-Q