Investments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) engine aircraft	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	May 25, 2011
Investments
Net book value of equipment held for operating lease	$ 1,466,144		$ 1,342,571
Investment in WMES joint ventures at beginning of the period	50,641
Earnings from joint venture	747
Deferred gain on engine sale	(723)
Foreign Currency Translation Adjustment	585
Investment in WMES joint ventures at end of the period	51,250
Revenue	$ 1,882
WMES
Investments
Number of engines in lease portfolio | engine	34
Number of aircraft in lease portfolio | aircraft	1
Net book value of equipment held for operating lease	$ 268,500
Ownership interest (as a percent)	100.00%			50.00%
Investment in WMES joint ventures at beginning of the period	$ 36,014
Earnings from joint venture	390
Deferred gain on engine sale	(723)
Investment in WMES joint ventures at end of the period	35,681
Condensed Consolidated Statements of Income
Revenue	7,606	$ 11,661
Expenses	6,904	8,430
WMES net income	702	3,231
Condensed Consolidated Balance Sheets
Total assets	273,952		246,309
Total liabilities	192,169		165,228
Total WMES net equity	81,783		$ 81,081
WMES | Other Revenue | Asset Management
Investments
Revenue	$ 700	$ 800
CASC Willis
Investments
Number of engines in lease portfolio | engine	4
Net book value of equipment held for operating lease	$ 58,800
Ownership interest (as a percent)	50.00%
Investment in WMES joint ventures at beginning of the period	$ 14,627
Earnings from joint venture	357
Foreign Currency Translation Adjustment	585
Investment in WMES joint ventures at end of the period	$ 15,569