Investments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) engine aircraft	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	May 25, 2011
Investments
Net book value of equipment held for operating lease	$ 1,542,329		$ 1,542,329		$ 1,342,571
Investment in WMES joint ventures at beginning of the period			50,641
Earnings from joint venture			1,063
Deferred gain on engine sale			(723)
Foreign Currency Translation Adjustment			(232)
Investment in WMES joint ventures at end of the period	50,749		$ 50,749
Revenue	1,871
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	$ 266,300		$ 266,300
Ownership interest (as a percent)	100.00%		100.00%			50.00%
Investment in WMES joint ventures at beginning of the period			$ 36,014
Earnings from joint venture			1,090
Deferred gain on engine sale			(723)
Investment in WMES joint ventures at end of the period	$ 36,381		36,381
Condensed Consolidated Statements of Income
Revenue	9,040	$ 8,199	16,646	$ 19,860
Expenses	7,551	6,700	14,354	15,129
WMES net income	1,489	1,499	2,292	4,731
Condensed Consolidated Balance Sheets
Total assets	282,826		282,826		246,309
Total liabilities	199,741		199,741		165,228
Total WMES net equity	83,085		83,085		$ 81,081
WMES | Other Revenue | Asset Management
Investments
Revenue	500	$ 500	$ 1,200	$ 1,300
CASC Willis
Investments
Number of engines in lease portfolio | engine			4
Net book value of equipment held for operating lease	$ 57,200		$ 57,200
Ownership interest (as a percent)	50.00%		50.00%
Investment in WMES joint ventures at beginning of the period			$ 14,627
Earnings from joint venture			(27)
Foreign Currency Translation Adjustment			(232)
Investment in WMES joint ventures at end of the period	$ 14,368		$ 14,368