Debt Obligations (Details) $ in Thousands				1 Months Ended	12 Months Ended
	Aug. 22, 2018 USD ($) NotesSeries	Aug. 04, 2017 USD ($) item	Jul. 16, 2014 USD ($)	Jan. 31, 2018 engine	Dec. 31, 2018 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2016 USD ($) item	Apr. 30, 2016 USD ($)
Long Term Debt
Maturity term		10 years
Percentage of the funding for the purchase of a corporate aircraft					100.00%
Principal outstanding repayable
2019					$ 55,380
2020					54,980
2021					482,217
2022					207,733
2023					34,008
Thereafter					524,112
Total					1,358,430		$ 1,103,743
Less: unamortized debt issuance costs					(21,081)		(18,338)
Total debt obligations					$ 1,337,349		$ 1,085,405
Gains (Losses) on Extinguishment of Debt						$ (137)
One-month LIBOR
Long Term Debt
One-month LIBOR rate (as a percent)					2.50%		1.57%
WEST III
Long Term Debt
Number of series notes | item		2
Credit facility at a floating rate of interest of one-month LIBOR plus 2.0% 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					$ 427,000		$ 491,000
WEST IV
Long Term Debt
Number of series notes | NotesSeries	2
Aggregate principal amount	$ 373,400
Line of credit facility outstanding amount					$ 369,200
WEST IV Series A 2018 term notes payable at a fixed rate of interest of 4.75%, maturing in September 2043, secured by engines
Long Term Debt
Fixed rate (as a percent)					4.75%
Notes issues at price of par (as percentage)	99.99853%
Aggregate principal amount	$ 326,800
Maturity term	8 years
Principal outstanding repayable
Total					$ 323,075
WEST IV Series B 2018 term notes payable at a fixed rate of interest of 5.44%, maturing in September 2043, secured by engines
Long Term Debt
Fixed rate (as a percent)					5.44%
Notes issues at price of par (as percentage)	99.99504%
Aggregate principal amount	$ 46,700
Maturity term	8 years
Principal outstanding repayable
Total					$ 46,154
WEST III
Long Term Debt
Line of credit facility outstanding amount					$ 313,400		330,700
WEST III Series A 2017 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					$ 274,205		289,295
WEST III Series A 2017 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 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					$ 39,212		41,370
WEST III Series B 2017 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 A 2012 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%
Line of credit facility outstanding amount					$ 173,800
Principal outstanding repayable
Total					$ 237,847		259,022
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					$ 10,937		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 one-month LIBOR plus 2.25%, matured in January 2018, secured by engines
Long Term Debt
Fixed rate (as a percent)					2.25%
Principal outstanding repayable
Total							10,336
Number of engines pledged as collateral | engine				3
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					$ 427,000
Principal outstanding repayable
Remaining borrowing capacity available					$ 463,000		$ 399,000
Maximum borrowing capacity under credit facility before amendment									$ 700,000