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Income Taxes (Summary of Unrecognized Tax Benefits and Temporary Differences) (Details) - USD ($) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Unrecognized tax benefits |  |  |  |  |  |
Balance at the beginning of the period |  | $ 191,000 | $ 206,000 | $ 274,000 | $ 464,000 |
Increases related to current year tax positions |  |  | 4,000 | 4,000 | 5,000 |
Decreases due to tax positions expired |  |  | (19,000) | (72,000) | (195,000) |
Balance at the end of the period | $ 191,000 |  | 191,000 | 206,000 | $ 274,000 |
Uncertain tax positions, reserved for tax exposure in Europe | 0 |  | 0 | 0 |  |
Deferred tax assets: |  |  |  |  |  |
Unearned lease revenue | 1,754,000 |  | 1,754,000 | 1,839,000 |  |
State taxes | 1,653,000 |  | 1,653,000 | 1,035,000 |  |
Reserves and allowances | 2,531,000 |  | 2,531,000 | 1,659,000 |  |
Other accruals | 643,000 |  | 643,000 | 2,501,000 |  |
Alternative minimum tax credit |  |  |  | 335,000 |  |
Foreign tax credit | 42,000 |  | 42,000 | 42,000 |  |
Net operating loss carry forward | 29,874,000 |  | 29,874,000 | 35,693,000 |  |
Charitable contributions | 22,000 |  | 22,000 | 52,000 |  |
Total deferred tax assets | 36,519,000 |  | 36,519,000 | 43,156,000 |  |
Less: valuation allowance | (806,000) |  | (806,000) | (1,280,000) |  |
Net deferred tax assets | 35,713,000 |  | 35,713,000 | 41,876,000 |  |
Deferred tax liabilities: |  |  |  |  |  |
Depreciation and impairment on aircraft engines and equipment | (114,347,000) |  | (114,347,000) | (147,827,000) |  |
Other deferred tax assets (liabilities) | 437,000 |  | 437,000 | 422,000 |  |
Net deferred tax liabilities | (113,910,000) |  | (113,910,000) | (147,405,000) |  |
Other comprehensive income, deferred tax asset | (83,000) |  | (83,000) | 551,000 |  |
Net deferred tax liabilities | (78,280,000) |  | $ (78,280,000) | $ (104,978,000) |  |
Valuation allowance of net operating loss |  |  |  |  |  | $ 1,300,000
Statutory federal income tax expense (as a percent) |  |  | 35.00% |  |  |
Additional income tax benefit | 39,600,000 |  |  |  |  |
Provisional amount | 43,600,000 |  |  |  |  |
Reduction in tax expenses | 4,000,000 |  |  |  |  |
Scenario, Forecast [Member] |  |  |  |  |  |
Deferred tax liabilities: |  |  |  |  |  |
Statutory federal income tax expense (as a percent) |  | 21.00% |  |  |  |
Federal |  |  |  |  |  |
Deferred tax assets: |  |  |  |  |  |
Alternative minimum tax credit | 400,000 |  | $ 400,000 |  |  |
Deferred tax liabilities: |  |  |  |  |  |
Operating loss carryforwards | 138,000,000 |  | 138,000,000 |  |  |
Valuation allowance of net operating loss | 0 |  | $ 0 |  |  |
Federal | Minimum |  |  |  |  |  |
Deferred tax liabilities: |  |  |  |  |  |
Alternative minimum tax credit period |  |  | 2 years |  |  |
Federal | Maximum |  |  |  |  |  |
Deferred tax liabilities: |  |  |  |  |  |
Alternative minimum tax credit period |  |  | 4 years |  |  |
State |  |  |  |  |  |
Deferred tax liabilities: |  |  |  |  |  |
Operating loss carryforwards | $ 1,000,000 |  | $ 1,000,000 |  |  |

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