Notes Payable (Details) - USD ($) $ in Thousands		6 Months Ended
	Apr. 20, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Apr. 19, 2016
Principal outstanding repayable
2017		$ 11,872
2018		33,294
2019		23,430
2020		23,031
2021		663,268
Thereafter		179,056
Notes payable		933,951		$ 913,703
Less: unamortized debt issuance costs		(12,169)		(13,448)
Total notes payable		921,782		$ 900,255
Net proceeds received from notes issued and sold		$ 93,000	$ 55,000
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		$ 269,336		$ 279,541
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		$ 13,592		14,453
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		$ 11,023		11,709
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		$ 640,000		$ 608,000
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%