Investments (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2014 USD ($)	Dec. 31, 2017 USD ($) engine	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	May 25, 2017	Jun. 03, 2014
Investments
Net book value of equipment held for operating lease		$ 1,342,571	$ 1,136,603
Ownership interest (as a percent)		50.00%
Investment in WMES joint ventures at beginning of the period		$ 45,406	41,295	$ 41,590
Investment			5,545	630
Earnings from joint venture		7,158	1,813	1,175
Deferred gain on engine sale		(939)	(1,212)
Distribution		(1,880)	(1,167)	(1,304)
Foreign Currency Translation Adjustment		(896)	(868)	(796)
Investment in WMES joint ventures at end of the period		50,641	45,406	41,295
Property Subject to or Available for Operating Lease, Net		1,342,571	1,136,603
Sale of engines		$ 43,791	62,525	41,608
WMES
Investments
Number of engines in lease portfolio | engine		32
Net book value of equipment held for operating lease		$ 230,300
Ownership interest (as a percent)		100.00%			50.00%
Investment in WMES joint ventures at beginning of the period		$ 32,470	27,272	26,672
Investment			5,545	630
Earnings from joint venture		5,867	2,032	1,274
Deferred gain on engine sale		(443)	(1,212)
Distribution		(1,880)	(1,167)	(1,304)
Investment in WMES joint ventures at end of the period		36,014	32,470	27,272
Property Subject to or Available for Operating Lease, Net		230,300
Engine Value		100
Consolidated Statements of Income
Revenue		40,211	35,463	26,909
Expenses		28,754	31,669	24,574
WMES net income		11,457	3,794	2,335
Consolidated Balance Sheets
Total assets		246,309	293,299
Total liabilities		165,228	219,881
Total WMES net equity		81,081	73,418
WMES | Other Revenue
Investments
Management fees		$ 2,400	2,100	1,700
CASC Willis
Investments
Number of engines in lease portfolio | engine		4
Net book value of equipment held for operating lease		$ 58,800
Investment in WMES joint ventures at beginning of the period		12,936	14,023	14,918
Earnings from joint venture		1,291	(219)	(99)
Deferred gain on engine sale		(496)
Foreign Currency Translation Adjustment		(896)	(868)	(796)
Investment in WMES joint ventures at end of the period		14,627	$ 12,936	$ 14,023
Property Subject to or Available for Operating Lease, Net		$ 58,800
CASC
Investments
Ownership interest (as a percent)						50.00%
Investment	$ 15,000