Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Data [Line Items]
Operating and Capital Leases Income Statement Lease Revenue	$ 313,856	$ 302,120	$ 281,939	$ 265,602	$ 259,547	$ 247,789	$ 158,333	$ 163,025	$ 1,163,517	$ 828,694	$ 707,839
Gross Profit	1,095	1,369	1,328	392	386	232	0	0	4,184	618	0
Net gain (loss) on sale of leasing equipment	10,749	10,263	9,639	5,161	(4,261)	(12,319)	(1,930)	(1,837)	35,812	(20,347)	2,013
Non-designated interest rate swaps									(1,397)	(4,405)	2,240
Net (loss) income	$ 207,160	$ 57,156	$ 45,671	$ 34,611	$ 22,778	$ (51,211)	$ 6,174	$ 8,742	$ 344,598	$ (13,517)	$ 111,089
Net income (loss) per common share—Basic	$ 2.59	$ 0.76	$ 0.62	$ 0.47	$ 0.31	$ (0.74)	$ 0.15	$ 0.22	$ 4.55	$ (0.24)	$ 2.75
Net income (loss) per common share—Diluted	$ 2.57	$ 0.75	$ 0.62	$ 0.47	$ 0.31	$ (0.74)	$ 0.15	$ 0.22	$ 4.52	$ (0.24)	$ 2.71