Income Taxes - Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Tax Credit Carryforwards	$ 10,004	$ 5,980
Deferred tax assets:
Income tax credits	155,670	871
Deferred revenue	6,824	5,957
Nondeductible accruals	14,691	10,107
Deferred manufacturing credits	0	258
Accrued maintenance	2,168	1,991
Equity compensation	2,592	2,392
Other	5,262	4,684
Valuation allowance	(254)	(454)
Deferred tax assets	196,957	31,786
Deferred tax liabilities:
Deferred gain (loss) on leases, net	1,672	1,605
Accrued rent	6,068	12,055
Prepaid expenses	793	754
Property, plant and equipment	481,847	298,703
Deferred financing costs	189	225
Accrued aircraft and engine maintenance	61,529	27,258
Deferred tax liabilities	552,098	340,600
Net deferred tax assets (liabilities)	$ (355,141)	$ (308,814)