Investments - Additional Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) aircraft. engine	Sep. 30, 2019 USD ($) engine aircraft.	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Net book value of equipment held for operating lease	$ 32,155		$ 32,155		$ 31,520
Loss on sale of engine			100
Assets Leased to Others
Schedule of Equity Method Investments [Line Items]
Net book value of equipment held for operating lease	$ 1,616,513		$ 1,616,513		$ 1,650,918
WMES
Schedule of Equity Method Investments [Line Items]
Ownership interest	50.00%		50.00%
Number of engines in lease portfolio | engine			36
Number of aircraft in lease portfolio | aircraft.			5
Number of engines sold | engine			1
Proceeds from sale of engine			$ 8,400
Number of aircrafts sold | aircraft.				5
Proceeds from sale of aircraft				$ 76,400
WMES | Assets Leased to Others
Schedule of Equity Method Investments [Line Items]
Net book value of equipment held for operating lease	$ 296,700		$ 296,700
CASC Willis
Schedule of Equity Method Investments [Line Items]
Ownership interest	50.00%		50.00%
Number of engines in lease portfolio | engine			4
Number of engines sold | engine			0	0
Number of aircrafts sold | aircraft.			0	0
CASC Willis | Assets Leased to Others
Schedule of Equity Method Investments [Line Items]
Net book value of equipment held for operating lease	$ 48,700		$ 48,700
Willis Aeronautical Services, Inc.
Schedule of Equity Method Investments [Line Items]
Number of engines sold | engine				1
Proceeds from sale of engine				$ 2,600
Other Income | WMES | Asset Management
Schedule of Equity Method Investments [Line Items]
Maintenance reserve revenue	$ 400	$ 700	$ 1,200	$ 1,800