Summary of Significant Accounting Policies (Policy)	3 Months Ended
Summary of Significant Accounting Policies (Policy)	Mar. 31, 2019
Summary of Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of presentation: The accompanying unaudited financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and with the instructions to Form 10‑Q as mandated by the Securities and Exchange Commission. The unaudited interim financial statements reflect all adjustments which are, in the opinion of the Managing Member, necessary for a fair statement of financial position and results of operations for the interim periods presented. All such adjustments are of a normal recurring nature. Operating results for the three months ended March 31, 2019 and 2018 are not necessarily indicative of the results to be expected for the full year. Certain prior period amounts may have been reclassified to conform to the current period presentation. These reclassifications had no significant effect on the reported financial position or results from operations. Footnote and tabular amounts are presented in thousands, except as to Units and per Unit data. In preparing the accompanying unaudited financial statements, the Company has reviewed, as determined necessary by the Managing Member, events that have occurred after March 31, 2019, up until the issuance of the financial statements. No events were noted which would require additional disclosure in the footnotes to the financial statements or adjustments thereto.
Cash and Cash Equivalents	Cash and cash equivalents: Cash and cash equivalents include cash in banks and cash equivalent investments such as U.S. Treasury instruments with original and/or purchased maturities of ninety days or less.
Use of Estimates	Use of estimates: The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from the estimates. Such estimates primarily relate to the determination of residual values at the end of the lease term and expected future cash flows used for impairment analysis purposes, and determination of the allowances for doubtful accounts.
Segment Reporting	Segment reporting: The Company is organized into one operating segment for the purpose of making operating decisions or assessing performance. Accordingly, the Company operates in one reportable operating segment in the United States. The primary geographic region in which the Company sought leasing opportunities was North America. All of the Company’s operating revenues for the three months ended March 31, 2019 and 2018, and long-lived tangible assets as of March 31, 2019 and December 31, 2018 relate to customers domiciled in the United States.
Accounts Receivable	Accounts receivable: Accounts receivable represent the amounts billed under operating lease contracts which are currently due to the Company. Allowances for doubtful accounts are typically established based upon their aging and historical charge off and collection experience and the creditworthiness of specifically identified lessees and borrowers, and invoiced amounts. Accounts receivable deemed uncollectible are generally charged off against the allowance on a specific identification basis. Recoveries of amounts that were previously written-off are recorded as other income in the period received. Accounts receivable are generally placed in a non-accrual status (i.e., no revenue is recognized) when payments are more than 90 days past due. Additionally, management periodically reviews the creditworthiness of companies with lease payments outstanding less than 90 days. Based upon management’s judgment, such leases may be placed in non-accrual status. Leases placed on non-accrual status are only returned to an accrual status when the account has been brought current and management believes recovery of the remaining unpaid receivable is probable. Until such time, revenues on operating leases are recognized on a cash basis.
Investment in Securities	Investment in securities: From time to time, the Company may purchase securities of its borrowers or receive warrants in connection with its lending arrangements. Purchased securities The Company’s investment securities registered for public sale are carried at fair value. The Company’s investment securities with readily determinable fair values are measured at fair value with any changes in fair value recognized in the Company’s results of operations. The Company’s investment securities that do not have readily determinable fair values are measured at cost minus impairment, and adjusted for changes in observable prices. Factors considered by the Managing Member in determining fair value include, but are not limited to, available financial information, the issuer’s ability to meet its current obligations and indications of the issuer’s subsequent ability to raise capital. Based upon the Company’s review of its portfolio, the Company recorded unrealized gain on investment in securities totaling $15 thousand and $31 thousand during the respective three months ended March 31, 2019 and 2018. Purchased securities totaled $136 thousand and $33 thousand as of March 31, 2019 and December 31, 2018, respectively. Warrants Warrants owned by the Company are not registered for public sale, but are considered derivatives and are reflected at an estimated fair value on the balance sheet as determined by the Managing Member. During the respective three months ended March 31, 2019 and 2018, the Company recorded unrealized gain on fair value adjustments for warrants totaling $0 and $8 thousand. As of March 31, 2019 and December 31, 2018, the estimated fair value of the Company’s portfolio of warrants amounted to $60 thousand and $153 thousand, respectively. During the first quarter of 2019, there was a net exercise of warrants in exchange of securities. No exercises of any kind occurred during the comparative prior year period.
Credit Risk	Credit risk: Financial instruments that potentially subject the Company to concentrations of credit risk include cash and cash equivalents, operating lease receivables, and accounts receivable. The Company places the majority of its cash deposits in non-interest bearing accounts with financial institutions that have no less than $10 billion in assets. Such deposits are insured up to $250,000. The remainder of the Fund’s cash is temporarily invested in U.S. Treasury denominated instruments. The concentration of such deposits and temporary cash investments is not deemed to create a significant risk to the Company. Accounts receivable represent amounts due from in various industries, related to equipment on operating leases.
Equipment on Operating Leases and Related Revenue Recognition	Equipment under operating leases, net and related revenue recognition: Equipment subject to operating leases is stated at cost. Depreciation is being recognized on a straight-line method over the terms of the related leases to the equipment’s estimated residual values. Off-lease equipment is generally not subject to depreciation. The Company depreciates all lease assets, in accordance with guidelines consistent with ASC 360‑20‑35‑3, over the periods of the lease terms contained in each asset’s respective lease contract to the estimated residual value at the end of the lease contract. All lease assets are purchased only concurrent with the execution of a lease commitment by the lessee. Thus, the original depreciation period corresponds with the term of the original lease. Once the term of an original lease contract is completed, the subject property is typically sold to the existing user, re-leased to the existing user, or, when off-lease, is held for sale. Assets which are re-leased continue to be depreciated using the terms of the new lease agreements and the estimated residual values at the end of the new lease terms, adjusted downward as necessary. Assets classified as held-for-sale are carried at the lower of carrying amount, or the fair value less cost to sell (ASC 360‑10‑35‑43). The Company does not use the equipment held in its portfolio, but holds it solely for lease and ultimate sale. In the course of marketing equipment that has come off-lease, management may determine at some point that re-leasing the assets may provide a superior return for investors and would then execute another lease. Upon entering into a new lease contract, management will estimate the residual value once again and resume depreciation. If, and when, the Company, at any time, determines that depreciation in value may have occurred with respect to an asset held-for-sale, the Company would review the value to determine whether a material reduction in value had occurred and recognize any appropriate impairment. All lease assets, including off-lease assets, are subject to the Company’s quarterly impairment analysis, as described below. Maintenance costs associated with the Fund’s portfolio of leased assets are expensed as incurred. Major additions and betterments are capitalized. Operating lease revenue is recognized on a straight-line basis over the term of the underlying leases. The initial lease terms will vary as to the type of equipment subject to the leases, the needs of the lessees and the terms to be negotiated, but initial leases are generally on terms from 36 to 120 months. The difference between rent received and rental revenue recognized is recorded as unearned operating lease income on the balance sheet. Operating leases are generally placed in a non-accrual status (i.e., no revenue is recognized) when payments are more than 90 days past due. Additionally, management considers the equipment underlying the lease contracts for impairment and periodically reviews the credit worthiness of all operating lessees with payments outstanding less than 90 days. Based upon management’s judgment, the related operating leases may be placed on non-accrual status. Leases placed on non-accrual status are only returned to an accrual status when the account has been brought current and management believes recovery of the remaining unpaid lease payments is probable. Until such time, revenues are recognized on a cash basis.
Initial Direct Costs	Initial direct costs: With the adoption of ASU No. 2016-02 certain costs associated with the execution of the company’s leases, which were previously capitalized and amortized over the life of their respective leases, are expensed as incurred. In 2018 and prior, the Company capitalized initial direct costs (“IDC”) associated with the origination of lease assets. IDC includes both internal costs (e.g., the costs of employees’ activities in connection with successful lease originations) and external broker fees incurred with such originations. The costs are amortized on a lease by lease basis based on actual contract term using a straight-line method for operating leases. Upon disposal of the underlying lease assets, both the initial direct costs and the associated accumulated amortization are relieved. Costs related to leases that are not consummated are not eligible for capitalization as initial direct costs and are expensed as acquisition expense.
Per Unit Data	Per Unit data: The Company issues only one class of Units, none of which are considered dilutive. Net income and distributions per Unit are based upon the weighted average number of Other Members Units outstanding during the period.
Fair Value Measurement	Fair Value Measurement: Fair value measurements and disclosures are based on a fair value hierarchy as determined by significant inputs used to measure fair value. The three levels of inputs within the fair value hierarchy are defined as follows: Level 1 – Quoted prices in active markets for identical assets or liabilities. An active market for the asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis, generally on a national exchange. Level 2 – Quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-based valuations in which all significant inputs are observable in the market. Level 3 – Valuation is modeled using significant inputs that are unobservable in the market. These unobservable inputs reflect the Company’s own estimates of assumptions that market participants would use in pricing the asset or liability. The Company’s valuation policy is determined by members of the Asset Management, Credit and Accounting departments. Whenever possible, the policy is to obtain quoted market prices in active markets to estimate fair values for recognition and disclosure purposes. Where quoted market prices in active markets are not available, fair values are estimated using discounted cash flow analyses, broker quotes, information from third party remarketing agents, third party appraisals of collateral and/or other valuation techniques. These techniques are significantly affected by certain of the Company’s assumptions, including discount rates and estimates of future cash flows. Potential taxes and other transaction costs are not considered in estimating fair values. As the Company is responsible for determining fair value, an analysis is performed on prices obtained from third parties. Such analysis is performed by asset management and credit department personnel who are familiar with the Company’s investments in equipment, and equity securities of venture companies. The analysis may include a periodic review of price fluctuations and validation of numbers obtained from a specific third party by reference to multiple representative sources.
Recent Accounting Pronouncements	Recent accounting pronouncements: In February 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2016-02, Leases. In July 2018, the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases and ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. In December 2018, the FASB issued ASU No. 2018-20, Leases (Topic 842), Narrow-Scope Improvements for Lessors. In March 2019, the FASB issued ASU No. 2019-01, Leases: Codification Improvements. Collectively referred to hereafter as ASU No. 2016-02, these standards set out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract to control an asset (i.e., lessees and lessors). The Company does not have any non-cancelable leases where it is a lessee. ASU No. 2016-02 requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales type leases, direct financing leases and operating leases. These standards were effective as of January 1, 2019. Upon adoption, we applied the package of practical expedients that has allowed us to not reassess (i) whether any expired or existing contracts are or contain leases, (ii) lease classification for any expired or existing leases and (iii) initial direct costs for any expired or existing leases. Furthermore, we applied the optional transition method in ASU No. 2018-11, which has allowed us to initially apply the new leases standard at the adoption date and recognize a cumulative effect adjustment to the opening balance of retained earnings in the adoption period, although we did not have an adjustment. Additionally, our leases met the criteria in ASU No. 2018-11 to not separate non-lease components from the related lease component; therefore, the accounting for these leases remained largely unchanged from the previous standard. The adoption of ASU No. 2016-02 and the related improvements did not have a material impact in our financial statements. Upon adoption, (i) amounts previously recognized as lessee reimbursements and other income, for the three months ended March 31, 2019, have been classified as lease or financing income, (ii) allowances for bad debts are now recognized as a direct reduction of operating lease income, and (iii) certain costs associated with the execution of our leases, which were previously capitalized and amortized over the life of their respective leases, are expensed as incurred. Subsequent to January 1, 2019, provisions for credit losses relating to operating leases are now included in lease income in the Company’s financial statements. Provisions for credit losses prior to January 1, 2019 were previously included in operating expenses in our financial statements and prior periods are not reclassified to conform to the current presentation. In June 2016, the FASB issued Accounting Standards Update 2016-13, Financial Instruments — Credit Losses (Topic 326) (“ASU 2016-13”). The main objective of this Update is to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. To achieve this objective, the amendments in this Update replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The amendments affect entities holding financial assets and net investment in leases that are not accounted for at fair value through net income. The amendments affect loans, debt securities, trade receivables, net investments in leases, off-balance-sheet credit exposures, reinsurance receivables, and any other financial assets not excluded from the scope that have the contractual right to receive cash. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2018. Management is currently evaluating the standard and expects the Update may potentially result in an increase in the allowance for credit losses given the change to estimated losses over the contractual life adjusted for expected prepayments. In November 2018, the FASB issued Accounting Standards Update 2018-19, Codification Improvements to Topic 326, Financial Instruments — Credit Losses (“ASU 2018-19”). The new standard clarifies certain aspects of the new current expected credit losses (CECL) impairment model in ASU 2016-13. The amendment clarifies that receivables arising from operating leases are within the scope of ASC 842, rather than ASC 326; however, it will be applicable to our note receivables and direct financing leases, if any. The effective date and transition requirements in this Update are the same as the effective dates and transition requirements in Update 2016-13, as amended by this Update, which is for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Management is currently evaluating the impact of the standard on the financial statements and related disclosure requirements. In August 2018, the FASB issued Accounting Standards Update 2018-13, Fair Value Measurement (“ASU 2018-13”), which amends the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurement. This ASU modifies disclosure requirements for fair value measurements by removing, modifying or adding certain disclosures. The amendments in this Update are effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. Early adoption is permitted upon issuance of this Update. An entity is permitted to early adopt any removed or modified disclosures upon issuance of this Update and delay adoption of the additional disclosures until their effective date. Management is currently evaluating the impact of this standard on the financial statements and related disclosure requirements. In August 2016, the FASB issued Accounting Standards Update 2016-15 — Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (“ASU 2016-15”). ASU 2016-15 addresses specific cash flow issues with the objective of reducing the existing diversity in practice. The amendments in this Update are effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. This guidance was adopted beginning on January 1, 2018. The adoption of ASU 2016-15 did not have a material impact on its financial statements and disclosures.

ATEL 12, LLC 10-Q