Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents, at Carrying Value	$ 152,719		$ 211,922		$ 455,579	$ 152,719	$ 211,922	$ 455,579
Restricted Cash and Cash Equivalents	15,134		21,935		53,238	15,134	21,935	53,238
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	167,853		233,857		508,817	167,853	233,857	508,817
Net income	103,837	$ 57,547	55,120	$ 42,439	151,453	247,919	147,874	151,453
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation					305,216	310,850	298,664	305,216
Amortization of deferred financing costs					18,508	14,627	19,435
Amortization of lease premiums, discounts and incentives					10,353	15,269	11,714	10,353
Deferred income taxes					6,156	(496)	(8,948)
Non-cash share-based payment expense					7,901	11,488	13,148	7,901
Cash flow hedges reclassified into earnings					9,662	1,166	2,202	9,662
Security deposits and maintenance payments included in earnings					(23,123)	(80,628)	(17,947)
Gain on the sale of flight equipment					(39,126)	(36,766)	(55,167)	(39,126)	$ (58,017)
Impairment of aircraft					28,585	0	80,430	28,585
Other					(6,867)	3,032	1,476
Changes on certain assets and liabilities:
Accounts receivable					832	(12,328)	(6,734)
Other assets					(1,089)	5,065	(7,655)
Accounts payable, accrued expenses and other liabilities					(4,014)	10,526	13,857
Lease rentals received in advance					3,645	32,868	(1,478)
Net Cash and Restricted Cash Provided by (Used in) Operating Activities					468,092	522,592	490,871
Cash flows from investing activities:
Acquisition and improvement of flight equipment					(1,331,059)	(1,317,497)	(1,038,343)
Proceeds from sale of flight equipment					755,898	338,831	833,576
Net investment in finance and sales-type leases					(78,892)	(15,783)	(331,721)
Proceeds from Collection of Finance Receivables					19,413	29,961	32,184
Aircraft purchase deposits and progress payments, net of returned deposits and aircraft sales deposits					(9,628)	(15,494)	(7,681)
Unconsolidated equity method investment and associated costs					(18,048)	(3,350)	0
Other					(839)	8,645	(5,122)
Net cash and restricted cash used in investing activities					(663,155)	(974,687)	(517,107)
Cash flows from financing activities:
Repurchase of shares					(37,337)	(71,421)	(4,862)
Proceeds from secured and unsecured debt financings					1,054,250	1,413,901	675,000
Repayments of secured and unsecured debt financings					(588,778)	(969,139)	(878,534)
Deferred financing costs					(18,890)	(11,642)	(8,540)
Restricted secured liquidity facility collateral					65,000	0	0
Liquidity facility					(65,000)	0	0
Security deposits and maintenance payments received					171,672	203,925	192,830
Security deposits and maintenance payments returned					(51,658)	(90,803)	(141,185)
Dividends paid					(77,137)	(88,730)	(83,433)
Other					(2,283)	0	0
Net cash and restricted cash provided by (used in) financing activities					449,839	386,091	(248,724)
Net (decrease) increase in cash and restricted cash					254,776	(66,004)	(274,960)
Cash and restricted cash at beginning of year		$ 233,857		$ 508,817		233,857	508,817	254,041
Cash and restricted cash at end of year	$ 167,853		$ 233,857		$ 508,817	167,853	233,857	508,817	$ 254,041
Supplemental disclosures of cash flow information:
Cash paid during the year for interest						214,350	228,125	224,705
Cash paid during the year for income taxes						6,254	4,576	16,693
Supplemental disclosures of non-cash investing activities:
Advance lease rentals, security deposits, maintenance payments, other liabilities and other assets settled in sale of flight equipment						71,837	132,585	75,335
Advance lease rentals, security deposits, maintenance payments, other liabilities and other assets assumed in asset acquisitions						63,432	149,100	202,808
Transfers from Flight equipment held for lease to Net investment in finance and sales-type leases and Other assets						$ 11,202	$ 154,213	$ 142,950