Debt Obligations (Details) $ in Thousands					12 Months Ended
	Aug. 04, 2017 USD ($) item	Mar. 25, 2015 USD ($)	Jul. 16, 2014 USD ($)	Jan. 10, 2014 engine	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2016 USD ($) item	Apr. 30, 2016 USD ($)
Long Term Debt
Maturity term	10 years
Maintenance Reserves					$ 75,889	$ 71,602
Percentage of the funding for the purchase of a corporate aircraft					100.00%
Principal outstanding repayable
2018					$ 48,401
2019					38,537
2020					38,137
2021					529,374
2022					190,889
Thereafter					258,405
Total					1,103,743	913,703
Less: unamortized debt issuance costs					(18,338)	(13,448)
Notes payable					$ 1,085,405	900,255
Gains (Losses) on Extinguishment of Debt						$ (137)	$ 1,151
One-month LIBOR
Long Term Debt
One-month LIBOR rate (as a percent)					1.57%	0.77%
WEST III
Long Term Debt
Number of series notes | item	2
Maintenance Reserves					$ 10,000
Credit facility at a floating rate of interest of one-month LIBOR plus 1.50% and maturity date of April 2021
Long Term Debt
Maximum borrowing capacity under credit facility					$ 890,000
Fixed rate (as a percent)					1.50%
Principal outstanding repayable
Total					$ 491,000	$ 608,000
WEST III
Long Term Debt
Line of credit facility outstanding amount					330,700
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
Principal outstanding repayable
Total					$ 289,295
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 | WEST III
Long Term Debt
Fixed rate (as a percent)					4.69%
Aggregate principal amount	$ 293,700
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
Principal outstanding repayable
Total					$ 41,370
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 | WEST III
Long Term Debt
Fixed rate (as a percent)					6.36%
Aggregate principal amount	$ 42,000
WEST II Series 2012-A term notes payable at a fixed rate of interest of 5.50%, maturing in September 2037, secured by engines
Principal outstanding repayable
Total					$ 259,022	279,541
WEST II Series 2012-A term notes payable at a fixed rate of interest of 5.50%, maturing in September 2037, secured by engines | WEST II
Long Term Debt
Fixed rate (as a percent)					5.50%
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft
Long Term Debt
Number of series notes | item								2
Aggregate principal amount			$ 13,400					$ 4,700
Maturity term			10 years
Initial term for interest payment					5 years
Principal outstanding repayable
Total					$ 12,720	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 variable interest rate of 2.25%, maturing in January 2018, secured by engines
Long Term Debt
Fixed rate (as a percent)					2.25%
Maturity term				4 years
Principal outstanding repayable
Total					$ 10,336	11,709
Number of engines pledged as collateral | engine				3
Note payable at a variable interest rate of 2.25%, maturing in January 2018, secured by engines | One-month LIBOR
Long Term Debt
Fixed rate (as a percent)				2.25%
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					491,000
Principal outstanding repayable
Remaining borrowing capacity available					$ 399,000	$ 282,000
Maximum borrowing capacity under credit facility before amendment									$ 700,000
Term notes | WOLF
Principal outstanding repayable
Loan Paid off		$ 23,100
Discount (in percentage)		5.00%
Gains (Losses) on Extinguishment of Debt							$ 1,200