Debt Obligations (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Principal outstanding repayable
2018	$ 28,622
2019	38,537
2020	38,137
2021	642,374
2022	190,889
Thereafter	258,405
Total	1,196,964	$ 1,103,743
Less: unamortized debt issuance costs	(17,307)	(18,338)
Total debt obligations	1,179,657	1,085,405
Credit facility at a floating rate of interest of one-month LIBOR plus 2% and maturity date of April 2021
Long Term Debt
Maximum borrowing capacity under credit facility	$ 890,000
Fixed rate (as a percent)	2.00%
Principal outstanding repayable
Total	$ 604,000	491,000
WEST III Series A 2017-1 term notes payable at a fixed rate of interest of 4.69%, maturing in August 2042. Secured by engines
Long Term Debt
Fixed rate (as a percent)	4.69%
Principal outstanding repayable
Total	$ 285,990	289,295
WEST III Series B 2017-1 term notes payable at a fixed rate of interest of 6.36%, maturing in August 2042. Secured by engines
Long Term Debt
Fixed rate (as a percent)	6.36%
Principal outstanding repayable
Total	$ 40,898	41,370
WEST II Series 2012-A term notes payable at a fixed rate of interest of 5.50%, maturing in September 2037, secured by engines
Long Term Debt
Fixed rate (as a percent)	5.50%
Principal outstanding repayable
Total	$ 253,798	259,022
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft
Principal outstanding repayable
Total	$ 12,278	12,720
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 variable interest rate of 2.25%, maturing in January 2018, secured by engines
Long Term Debt
Fixed rate (as a percent)	2.25%
Principal outstanding repayable
Total		$ 10,336
Revolving credit facility
Long Term Debt
Maximum borrowing capacity under credit facility	$ 890,000
Amount of debt available under accordion feature	1,000,000
Line of credit facility outstanding amount	$ 604,000