Notes Payable (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
	Apr. 20, 2016	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Apr. 19, 2016
Principal outstanding repayable
2016		$ 17,091
2017		23,624
2018		33,294
2019		562,430
2020		23,031
Thereafter		202,325
Notes payable		861,795		$ 878,684
Notes payable		861,795		878,684
Less: unamortized debt issuance costs		(11,764)		(12,595)
Total notes payable		850,031		866,089
Notes payable		850,031		$ 866,089
Net proceeds received from notes issued and sold		$ 20,000	$ 31,000
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		$ 294,337		$ 300,467
Notes payable		294,337		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		15,719		16,135
Notes payable		$ 15,719		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		$ 12,739		13,082
Notes payable		$ 12,739		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
Maximum borrowing capacity under credit facility					$ 700,000
Revolving credit facility | Subsequent event
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
Revolving credit facility | Subsequent event | LIBOR
Long Term Debt
Basis spread on variable rate (as a percent)	2.75%
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		$ 700,000
Principal outstanding repayable
Notes payable		539,000		549,000
Notes payable		$ 539,000		$ 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%