Organization and Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2018
Organization and Summary of Significant Accounting Policies [Abstract]
Organization and Summary of Significant Accounting Policies	1. Organization and Summary of Significant Accounting Policies (a) The Company and Basis of Presentation AeroCentury Corp., a Delaware corporation incorporated in 1997, typically acquires used regional aircraft for lease to foreign and domestic regional carriers. In August 2016, AeroCentury Corp. formed two wholly-owned subsidiaries, ACY SN 19002 Limited ("ACY 19002") and ACY SN 19003 Limited ("ACY 19003") for the purpose of acquiring aircraft using a combination of cash and third-party financing ("SPE Financing" or "special purpose financing") separate from the parent's credit facility (the "Credit Facility"). Financial information for AeroCentury Corp., ACY 19002 and ACY 19003 (collectively, the "Company") is presented on a consolidated basis in accordance with accounting principles generally accepted in the United States of America ("GAAP") for interim financial information, the instructions to Form 10-Q and Article 8 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for the three- and nine-month periods ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 or for any other period. All intercompany balances and transactions have been eliminated in consolidation. As discussed in Note 7, the Company's acquisition of JetFleet Holding Corp. ("JHC") was consummated on October 1, 2018. As a subsidiary of the Company, JHC's results will be included in the Company's consolidated financial statements beginning in the fourth quarter of 2018. For further information, refer to the financial statements and footnotes thereto included in the Company's annual report on Form 10-K for the year ended December 31, 2017. (b) Use of Estimates The Company's condensed consolidated financial statements have been prepared in accordance with GAAP. The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable for making judgments that are not readily apparent from other sources. The most significant estimates with regard to these condensed consolidated financial statements are the residual values and useful lives of the Company's long-lived assets, the amount and timing of future cash flows associated with each asset that are used to evaluate whether assets are impaired, accrued maintenance costs, accounting for income taxes, and the amounts recorded as allowances for doubtful accounts. (c) Fair Value Measurements Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs, to the extent possible. The fair value hierarchy under GAAP is based on three levels of inputs. Level 1 - Quoted prices in active markets for identical assets or liabilities. Level 2 - Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and Liabilities Measured and Recorded at Fair Value on a Recurring Basis The carrying amount of the Company's money market funds included in cash and cash equivalents was $2,155,600 and $6,151,900 at September 30, 2018 and December 31, 2017, respectively. The fair value of the Company's money market funds is categorized as Level 1 under the GAAP fair value hierarchy. As of September 30, 2018 and December 31, 2017, there were no liabilities that were required to be measured and recorded at fair value on a recurring basis. Assets Measured and Recorded at Fair Value on a Nonrecurring Basis The Company determines fair value of long-lived assets held and used, such as aircraft and aircraft engines held for lease and these and other assets held for sale, by reference to independent appraisals, quoted market prices (e.g., offers to purchase) and other factors. An impairment charge is recorded when the Company believes that the carrying value of an asset will not be recovered through future net cash flows and that the asset's carrying value exceeds its fair value. The Company recorded impairment charges totaling $2,673,300 on four of its aircraft held for sale in the three months ended September 30, 2018. The Company also recorded an impairment charge of $298,200 on one of its aircraft held for lease in the quarter ended June 30, 2018. The Company recorded an impairment charge of $68,800 on one of its assets held for lease in the quarter ended September 30, 2017, based on expected sales proceeds. The aircraft was sold in October 2017. The Company also recorded an impairment charge of $454,300 on one of its assets in the quarter ended June 30, 2017, based on its appraised value. Fair Value of Other Financial Instruments The Company's financial instruments, other than cash and cash equivalents, consist principally of finance leases receivable, amounts borrowed under the Credit Facility and notes payable under special purpose financing. The fair value of accounts receivable, accounts payable and the Company's maintenance reserves and accrued maintenance costs approximates the carrying value of these financial instruments because of their short-term maturities. The fair value of finance lease receivables approximates the carrying value as discussed in (d) below. Borrowings under the Company's Credit Facility bear floating rates of interest that reset periodically to a market benchmark rate plus a credit margin. The Company believes the effective interest rate under the Credit Facility approximates current market rates for such indebtedness at the balance sheet date, and therefore that the outstanding principal and accrued interest of $131,004,800 and $134,278,900 at September 30, 2018 and December 31, 2017, respectively, approximate their fair values on such dates. The fair value of the Company's outstanding balance of its Credit Facility is categorized as Level 3 under the GAAP fair value hierarchy. The amounts payable under the Company's SPE Financing are payable through the fourth quarter of 2020 and bear a fixed rate of interest, as described in Note 4(b) to the condensed consolidated financial statements. The Company believes that the effective interest rate under the special purpose financing approximates current market rates for such indebtedness at the balance sheet date, and therefore that the outstanding principal and accrued interest of $10,321,300 and $13,535,300 approximate their fair values at September 30, 2018 and December 31, 2017, respectively. Such fair value is categorized as Level 3 under the GAAP fair value hierarchy. (d) Finance Leases As of September 30, 2018, the Company had three aircraft subject to sales-type finance leases and three aircraft subject to direct financing leases. All six leases contain lessee bargain purchase options at prices substantially below the subject assets' estimated residual values at the exercise date for the options. Consequently, the Company has classified each of these six leases as finance leases for financial accounting purposes. For such finance leases, the Company reports the discounted present value of (i) future minimum lease payments (including the bargain purchase option) and (ii) any residual value not subject to a bargain purchase option as a finance lease receivable on its balance sheet and accrues interest on the balance of the finance lease receivable based on the interest rate inherent in the applicable lease over the term of the lease. For each of the three sales-type finance leases, the Company recognized as a gain or loss the amount equal to (i) the net investment in the sales-type finance lease plus any initial direct costs and lease incentives less (ii) the net book value of the subject aircraft at inception of the applicable lease. The Company recognized interest earned on finance leases in the amount of $261,700 and $415,700 in the quarters ended September 30, 2018 and 2017, respectively and $1,002,100 and $1,173,400 in the nine-month periods ended September 30, 2018 and 2017, respectively. (e) Recent Accounting Pronouncements Topic 606 In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09 that created the new Topic 606 ("Topic 606") in the Accounting Standards Codification ("ASC"). Topic 606 also included numerous conforming additions and amendments to other Topics within the ASC. Topic 606 established new rules that affect the amount and timing of revenue recognition for contracts with customers, but does not affect lease accounting and reporting. As such, adoption of these provisions has not affected the Company's lease revenues. On August 12, 2015, the FASB deferred the effective date of the provisions included in Topic 606 to years commencing after December 15, 2017, although early adoption was permitted for the year ended December 31, 2017. As such, the Company adopted Topic 606 as of January 1, 2018. Adoption may be reflected using either a full retrospective method, applying the standard to all periods presented, or a simplified method that does not recast prior periods but does disclose the effect of the adoption on the current period condensed consolidated financial statements. Since most of the Company's revenues arise from its lease contracts, which are not affected by the new standard, and since the Company's revenue recognition for other sources of revenue is generally the same as it was under previous accounting standards, adoption of Topic 606 in the current year, using the modified retrospective approach, has had no effect on its condensed consolidated financial statements. ASU 2016-02 In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) ("ASU 2016-02"). ASU 2016-02 is effective for public companies for years beginning after December 15, 2018, although early adoption is permitted. ASU 2016-02 substantially modifies lessee accounting for leases, requiring that lessees recognize lease assets and liabilities for leases extending beyond one year. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new standard requires a lessor to classify leases as sales-type, finance, or operating. A lease will be treated as sales-type if it transfers all of the risks and rewards, as well as control of the underlying asset, to the lessee. If risks and rewards are conveyed without the transfer of control, the lease is treated as a financing. If the lessor does not convey risks and rewards or control, an operating lease results. A modified retrospective transition approach is required for lessors for sales-type, finance, and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. The Company is reviewing those agreements under which it is the lessor and is evaluating the impact of the adoption of ASU 2016-02 on its condensed consolidated financial statements and related disclosures. The Company does not expect to adopt ASU 2016-02 early, and expects to elect practical expedients in connection with its adoption, including not re-evaluating lease classification or capitalized initial direct costs on existing leases. As of September 30, 2018, the Company was not a lessee under any agreements that would be considered leases under ASU 2016-02, and so would be unaffected with respect to its adoption with respect to lessee accounting. As a result of the Company's acquisition of JHC on October 1, 2018, the Company became a lessee under a real estate lease and will need to evaluate reporting for that lease under ASU 2016-02. ASU 2017-01 In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805) ("ASU 2017-01"). ASU 2017-01 is effective for public companies for years beginning after December 15, 2017, although early adoption is permitted. ASU 2017-01 clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The Company adopted ASU 2017-01 effective beginning the quarter ended March 31, 2017, and determined that none of its acquired assets qualify as a business, such that no gain, loss or adjustment to the carrying value of assets was required in connection with such adoption. ASU 2017-04 In January 2017, the FASB issued ASU 2017-04, Intangibles -- Goodwill and Other (Topic 350) ("ASU 2017-04"), which provides for simplification of the test for goodwill impairment. Under the revised standard, "step 2" of the test under the previous standard is eliminated and (i) the fair value of the reporting unit is compared to its carrying value, with (ii) an impairment charge up to the amount of goodwill recognized for the excess of carrying value over fair value (considering the income tax effects of deductible goodwill, if applicable). The new provisions are required to be adopted for fiscal years beginning after December 15, 2019, although the Company has elected to early adopt the new provisions beginning with its quarter ended March 31, 2017. Adoption of ASU 2017-04 has had no effect on the financial results or position of the Company. SAB 118 In December of 2017, the United States enacted the Tax Cuts and Jobs Act of 2017 (the "Tax Act"), which had numerous effects on U.S. corporate taxation, including reducing the federal corporate tax rate to 21%, substantially modifying the U.S. taxation of international investments and transactions, and repealing the alternative minimum tax. In December of 2017, the Staff of the SEC issued Staff Accounting Bulletin No. 118 ("SAB 118"), which provides that companies should reflect in their financial statements the effects of the change in tax law in which the accounting is complete, as such completion occurs; provisional amounts for such effects for which the company can determine a reasonable estimate, as such estimates can be made; and continued accounting under the provisions of the law as it existed before enactment of the Tax Act for such effects for which no reasonable estimate under the new law can be made, until such a reasonable estimate is available and a provisional amount can be reported. Under SAB 118, in no event should the period during which a company is obtaining, preparing, and analyzing the information needed to complete the accounting for the effects of the change in tax law exceed one year from enactment (the "measurement period"), or the fourth quarter of 2018. The Company has reflected the effects of the Tax Act in these condensed consolidated financial statements and does not expect further analysis will be required.

1. Organization and Summary of Significant Accounting Policies

(a) The Company and Basis of Presentation

AeroCentury Corp., a Delaware corporation incorporated in 1997, typically acquires used regional aircraft for lease to foreign and domestic regional carriers.

In August 2016, AeroCentury Corp. formed two wholly-owned subsidiaries, ACY SN 19002 Limited ("ACY 19002") and ACY SN 19003 Limited ("ACY 19003") for the purpose of acquiring aircraft using a combination of cash and third-party financing ("SPE Financing" or "special purpose financing") separate from the parent's credit facility (the "Credit Facility"). Financial information for AeroCentury Corp., ACY 19002 and ACY 19003 (collectively, the "Company") is presented on a consolidated basis in accordance with accounting principles generally accepted in the United States of America ("GAAP") for interim financial information, the instructions to Form 10-Q and Article 8 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for the three- and nine-month periods ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 or for any other period. All intercompany balances and transactions have been eliminated in consolidation.

As discussed in Note 7, the Company's acquisition of JetFleet Holding Corp. ("JHC") was consummated on October 1, 2018. As a subsidiary of the Company, JHC's results will be included in the Company's consolidated financial statements beginning in the fourth quarter of 2018.

For further information, refer to the financial statements and footnotes thereto included in the Company's annual report on Form 10-K for the year ended December 31, 2017.

(b) Use of Estimates

The Company's condensed consolidated financial statements have been prepared in accordance with GAAP. The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable for making judgments that are not readily apparent from other sources.

The most significant estimates with regard to these condensed consolidated financial statements are the residual values and useful lives of the Company's long-lived assets, the amount and timing of future cash flows associated with each asset that are used to evaluate whether assets are impaired, accrued maintenance costs, accounting for income taxes, and the amounts recorded as allowances for doubtful accounts.

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs, to the extent possible. The fair value hierarchy under GAAP is based on three levels of inputs.

Level 1 - Quoted prices in active markets for identical assets or liabilities.

Level 2 - Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Assets and Liabilities Measured and Recorded at Fair Value on a Recurring Basis

The carrying amount of the Company's money market funds included in cash and cash equivalents was $2,155,600 and $6,151,900 at September 30, 2018 and December 31, 2017, respectively. The fair value of the Company's money market funds is categorized as Level 1 under the GAAP fair value hierarchy.

As of September 30, 2018 and December 31, 2017, there were no liabilities that were required to be measured and recorded at fair value on a recurring basis.

Assets Measured and Recorded at Fair Value on a Nonrecurring Basis

The Company determines fair value of long-lived assets held and used, such as aircraft and aircraft engines held for lease and these and other assets held for sale, by reference to independent appraisals, quoted market prices (e.g., offers to purchase) and other factors. An impairment charge is recorded when the Company believes that the carrying value of an asset will not be recovered through future net cash flows and that the asset's carrying value exceeds its fair value. The Company recorded impairment charges totaling $2,673,300 on four of its aircraft held for sale in the three months ended September 30, 2018. The Company also recorded an impairment charge of $298,200 on one of its aircraft held for lease in the quarter ended June 30, 2018. The Company recorded an impairment charge of $68,800 on one of its assets held for lease in the quarter ended September 30, 2017, based on expected sales proceeds. The aircraft was sold in October 2017. The Company also recorded an impairment charge of $454,300 on one of its assets in the quarter ended June 30, 2017, based on its appraised value.

Fair Value of Other Financial Instruments

The Company's financial instruments, other than cash and cash equivalents, consist principally of finance leases receivable, amounts borrowed under the Credit Facility and notes payable under special purpose financing. The fair value of accounts receivable, accounts payable and the Company's maintenance reserves and accrued maintenance costs approximates the carrying value of these financial instruments because of their short-term maturities. The fair value of finance lease receivables approximates the carrying value as discussed in (d) below.

Borrowings under the Company's Credit Facility bear floating rates of interest that reset periodically to a market benchmark rate plus a credit margin. The Company believes the effective interest rate under the Credit Facility approximates current market rates for such indebtedness at the balance sheet date, and therefore that the outstanding principal and accrued interest of $131,004,800 and $134,278,900 at September 30, 2018 and December 31, 2017, respectively, approximate their fair values on such dates. The fair value of the Company's outstanding balance of its Credit Facility is categorized as Level 3 under the GAAP fair value hierarchy.

The amounts payable under the Company's SPE Financing are payable through the fourth quarter of 2020 and bear a fixed rate of interest, as described in Note 4(b) to the condensed consolidated financial statements. The Company believes that the effective interest rate under the special purpose financing approximates current market rates for such indebtedness at the balance sheet date, and therefore that the outstanding principal and accrued interest of $10,321,300 and $13,535,300 approximate their fair values at September 30, 2018 and December 31, 2017, respectively. Such fair value is categorized as Level 3 under the GAAP fair value hierarchy.

(d) Finance Leases

As of September 30, 2018, the Company had three aircraft subject to sales-type finance leases and three aircraft subject to direct financing leases. All six leases contain lessee bargain purchase options at prices substantially below the subject assets' estimated residual values at the exercise date for the options. Consequently, the Company has classified each of these six leases as finance leases for financial accounting purposes. For such finance leases, the Company reports the discounted present value of (i) future minimum lease payments (including the bargain purchase option) and (ii) any residual value not subject to a bargain purchase option as a finance lease receivable on its balance sheet and accrues interest on the balance of the finance lease receivable based on the interest rate inherent in the applicable lease over the term of the lease. For each of the three sales-type finance leases, the Company recognized as a gain or loss the amount equal to (i) the net investment in the sales-type finance lease plus any initial direct costs and lease incentives less (ii) the net book value of the subject aircraft at inception of the applicable lease.

The Company recognized interest earned on finance leases in the amount of $261,700 and $415,700 in the quarters ended September 30, 2018 and 2017, respectively and $1,002,100 and $1,173,400 in the nine-month periods ended September 30, 2018 and 2017, respectively.

(e) Recent Accounting Pronouncements

Topic 606

In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09 that created the new Topic 606 ("Topic 606") in the Accounting Standards Codification ("ASC"). Topic 606 also included numerous conforming additions and amendments to other Topics within the ASC. Topic 606 established new rules that affect the amount and timing of revenue recognition for contracts with customers, but does not affect lease accounting and reporting. As such, adoption of these provisions has not affected the Company's lease revenues. On August 12, 2015, the FASB deferred the effective date of the provisions included in Topic 606 to years commencing after December 15, 2017, although early adoption was permitted for the year ended December 31, 2017. As such, the Company adopted Topic 606 as of January 1, 2018. Adoption may be reflected using either a full retrospective method, applying the standard to all periods presented, or a simplified method that does not recast prior periods but does disclose the effect of the adoption on the current period condensed consolidated financial statements. Since most of the Company's revenues arise from its lease contracts, which are not affected by the new standard, and since the Company's revenue recognition for other sources of revenue is generally the same as it was under previous accounting standards, adoption of Topic 606 in the current year, using the modified retrospective approach, has had no effect on its condensed consolidated financial statements.

ASU 2016-02

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) ("ASU 2016-02"). ASU 2016-02 is effective for public companies for years beginning after December 15, 2018, although early adoption is permitted. ASU 2016-02 substantially modifies lessee accounting for leases, requiring that lessees recognize lease assets and liabilities for leases extending beyond one year. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement.

The new standard requires a lessor to classify leases as sales-type, finance, or operating. A lease will be treated as sales-type if it transfers all of the risks and rewards, as well as control of the underlying asset, to the lessee. If risks and rewards are conveyed without the transfer of control, the lease is treated as a financing. If the lessor does not convey risks and rewards or control, an operating lease results. A modified retrospective transition approach is required for lessors for sales-type, finance, and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. The Company is reviewing those agreements under which it is the lessor and is evaluating the impact of the adoption of ASU 2016-02 on its condensed consolidated financial statements and related disclosures. The Company does not expect to adopt ASU 2016-02 early, and expects to elect practical expedients in connection with its adoption, including not re-evaluating lease classification or capitalized initial direct costs on existing leases.

As of September 30, 2018, the Company was not a lessee under any agreements that would be considered leases under ASU 2016-02, and so would be unaffected with respect to its adoption with respect to lessee accounting. As a result of the Company's acquisition of JHC on October 1, 2018, the Company became a lessee under a real estate lease and will need to evaluate reporting for that lease under ASU 2016-02.

ASU 2017-01

In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805) ("ASU 2017-01"). ASU 2017-01 is effective for public companies for years beginning after December 15, 2017, although early adoption is permitted. ASU 2017-01 clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The Company adopted ASU 2017-01 effective beginning the quarter ended March 31, 2017, and determined that none of its acquired assets qualify as a business, such that no gain, loss or adjustment to the carrying value of assets was required in connection with such adoption.

ASU 2017-04

In January 2017, the FASB issued ASU 2017-04, Intangibles -- Goodwill and Other (Topic 350) ("ASU 2017-04"), which provides for simplification of the test for goodwill impairment. Under the revised standard, "step 2" of the test under the previous standard is eliminated and (i) the fair value of the reporting unit is compared to its carrying value, with (ii) an impairment charge up to the amount of goodwill recognized for the excess of carrying value over fair value (considering the income tax effects of deductible goodwill, if applicable). The new provisions are required to be adopted for fiscal years beginning after December 15, 2019, although the Company has elected to early adopt the new provisions beginning with its quarter ended March 31, 2017. Adoption of ASU 2017-04 has had no effect on the financial results or position of the Company.

SAB 118

In December of 2017, the United States enacted the Tax Cuts and Jobs Act of 2017 (the "Tax Act"), which had numerous effects on U.S. corporate taxation, including reducing the federal corporate tax rate to 21%, substantially modifying the U.S. taxation of international investments and transactions, and repealing the alternative minimum tax. In December of 2017, the Staff of the SEC issued Staff Accounting Bulletin No. 118 ("SAB 118"), which provides that companies should reflect in their financial statements the effects of the change in tax law in which the accounting is complete, as such completion occurs; provisional amounts for such effects for which the company can determine a reasonable estimate, as such estimates can be made; and continued accounting under the provisions of the law as it existed before enactment of the Tax Act for such effects for which no reasonable estimate under the new law can be made, until such a reasonable estimate is available and a provisional amount can be reported. Under SAB 118, in no event should the period during which a company is obtaining, preparing, and analyzing the information needed to complete the accounting for the effects of the change in tax law exceed one year from enactment (the "measurement period"), or the fourth quarter of 2018. The Company has reflected the effects of the Tax Act in these condensed consolidated financial statements and does not expect further analysis will be required.