Investments (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jun. 03, 2014
Investments
Investment in WMES joint ventures at beginning of the period		$ 41,295	$ 41,590
Investment		5,545	630	$ 17,623
Earnings from joint venture		1,813	1,175
Distribution		(1,167)	(1,304)
Foreign Currency Translation Adjustment		868	(796)
Investment in WMES joint ventures at end of the period		45,406	41,295	41,590
Amortization of deferred gain		(1,212)
Property Subject to or Available for Operating Lease, Net	$ 49,100				$ 1,136,603	$ 1,109,168	$ 1,057,381
Equity Method Investments		41,295	41,590	41,590	$ 45,406	41,295	41,590
WMES
Investments
Ownership interest (as a percent)					50.00%
Investment in WMES joint ventures at beginning of the period		27,272	26,672
Investment		5,545	630
Earnings from joint venture		2,032	1,274
Distribution		(1,167)	(1,304)
Investment in WMES joint ventures at end of the period		32,470	27,272	26,672
Amortization of deferred gain		(1,212)
Equity Method Investments		27,272	26,672	26,672	$ 32,470	27,272	26,672
Engine Value					100
Consolidated Statements of Income
Revenue		35,463	26,909	25,757
Expenses		31,669	24,574	23,150
WMES net income		3,794	2,335	2,607
Consolidated Balance Sheets
Total assets					293,299	256,126
Total liabilities					219,881	195,258
Total WMES net equity					73,418	60,868
WMES | Other Revenue
Investments
Management fees		2,100	1,700	2,000
CASC Willis
Investments
Investment in WMES joint ventures at beginning of the period		14,023	14,918
Earnings from joint venture		(219)	(99)
Foreign Currency Translation Adjustment		868	(796)
Investment in WMES joint ventures at end of the period		12,936	14,023	14,918
Equity Method Investments		14,023	$ 14,918	$ 14,918	12,936	$ 14,023	$ 14,918
CASC
Investments
Ownership interest (as a percent)								50.00%
Investment	$ 15,000
Investment in WMES joint ventures at end of the period		12,900
Equity Method Investments		$ 12,900			$ 12,900