Notes Payable (Details) - USD ($) $ in Thousands		6 Months Ended
	Apr. 20, 2016	Jun. 30, 2016	Jun. 30, 2015	Apr. 19, 2016	Dec. 31, 2015
Principal outstanding repayable
2016		$ 11,480
2017		23,624
2018		33,294
2019		23,430
2020		23,031
Thereafter		776,324
Notes payable		891,183			$ 878,684
Notes payable		891,183			878,684
Less: unamortized debt issuance costs		(14,477)			(12,595)
Total notes payable		876,706			866,089
Notes payable		876,706			$ 866,089
Net proceeds received from notes issued and sold		$ 55,000	$ 118,700
WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines | WEST II
Long Term Debt
Fixed rate (as a percent)		5.50%			5.50%
Principal outstanding repayable
Notes payable		$ 289,488			$ 300,467
Notes payable		289,488			300,467
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft
Principal outstanding repayable
Notes payable		15,300			16,135
Notes payable		$ 15,300			16,135
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft | Minimum
Long Term Debt
Fixed rate (as a percent)		2.60%
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft | Maximum
Long Term Debt
Fixed rate (as a percent)		2.97%
Note payable at a fixed interest rate of 2.25%, maturing in January 2018, secured by engines
Principal outstanding repayable
Notes payable		$ 12,395			13,082
Notes payable		$ 12,395			13,082
Note payable at a fixed interest rate of 2.25%, maturing in January 2018, secured by engines | LIBOR
Long Term Debt
Basis spread on variable rate (as a percent)		2.25%
Revolving credit facility
Long Term Debt
Basis spread on variable rate (as a percent)	2.75%
Maximum borrowing capacity under credit facility	$ 890,000			$ 700,000
Amount of debt available under accordion feature	$ 1,000,000
Credit facility at a floating rate of interest of LIBOR plus 2.75%, secured by engines
Long Term Debt
Maximum borrowing capacity under credit facility		$ 890,000
Principal outstanding repayable
Notes payable		574,000			549,000
Notes payable		$ 574,000			$ 549,000
Credit facility at a floating rate of interest of LIBOR plus 2.75%, secured by engines | LIBOR
Long Term Debt
Basis spread on variable rate (as a percent)		2.75%