Notes Payable (Details)										12 Months Ended
	Jul. 10, 2015 USD ($)	Mar. 25, 2015 USD ($)	Dec. 31, 2014 USD ($) item	Jul. 16, 2014 USD ($)	Jun. 04, 2014 USD ($)	Jan. 10, 2014 engine	Sep. 18, 2013 USD ($)	Sep. 28, 2012 USD ($)	Sep. 17, 2012 USD ($) engine	Dec. 31, 2015 USD ($) engine item	Dec. 31, 2014 USD ($) item	Dec. 31, 2013 USD ($)	Jun. 30, 2015 USD ($) item
Long Term Debt
Notes payable			$ 840,956,000							$ 878,684,000	$ 840,956,000
One-month LIBOR rate (as a percent)			0.17%							0.43%	0.17%
Principal outstanding repayable
2016										$ 22,702,000
2017										23,718,000
2018										33,391,000
2019 (includes $549.0 million outstanding on revolving credit facility)										572,529,000
2020										23,127,000
Thereafter										203,217,000
Notes payable			$ 840,956,000							878,684,000	$ 840,956,000
Line of credit facility outstanding amount										549,000,000
Notes payable			$ 840,956,000							878,684,000	840,956,000
Net proceeds received from notes issued and sold										$ 192,700,000	$ 154,395,000	$ 130,000,000
WOLF
Principal outstanding repayable
Acquisition of remaining outstanding shares of previously held equity method investment (as a percent)							50.00%
Controlling interest assumed (as a percent)							100.00%
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%	5.50%
Notes payable			$ 351,899,000							$ 300,467,000	$ 351,899,000
Principal outstanding repayable
Notes payable			351,899,000							$ 300,467,000	351,899,000
Maturity term										10 years
Face amount									$ 390,000,000
Net proceeds received from notes issued and sold									384,900,000
Number of engines in portfolio offered as collateral | item										63
Number of business days to pay interest										5 days
WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines | WEST II | Minimum
Principal outstanding repayable
Minimum amount of cash from maintenance reserve payments required to be held in restricted cash account										$ 9,000,000
Note payable at fixed interest rates ranging from 2.60% to 2.97%, maturing in July 2024. Secured by an aircraft
Long Term Debt
Initial term for interest payment										5 years
Notes payable			12,909,000							$ 16,135,000	12,909,000
Principal outstanding repayable
Notes payable			12,909,000							$ 16,135,000	12,909,000
Maturity term				10 years
Face amount				$ 13,400,000									$ 4,700,000
Number of term notes held | item													2
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
Long Term Debt
Notes payable			14,455,000							$ 13,082,000	14,455,000
Principal outstanding repayable
Notes payable			14,455,000							$ 13,082,000	$ 14,455,000
Maturity term						4 years
Number of engines pledged as collateral | engine						3
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%
Note payable at a fixed 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%
Note payable at a fixed interest rate of 4.00%, maturing in March 2015, secured by engines
Long Term Debt
Basis spread on variable rate (as a percent)											4.00%
Notes payable			24,000,000								$ 24,000,000
Principal outstanding repayable
Notes payable			24,000,000								24,000,000
Note payable at a fixed interest rate of 5.50%, maturing in July 2015. Secured by one engin.
Long Term Debt
Fixed rate (as a percent)										5.50%
Notes payable			7,693,000								7,693,000
Principal outstanding repayable
Notes payable			$ 7,693,000								$ 7,693,000
Maturity term								5 years
Face amount								$ 8,700,000
Loan Paid off	$ 7,400,000
Number of engines pledged as collateral | engine										1
Prior WEST notes
Long Term Debt
Notes payable									435,900,000
Principal outstanding repayable
Notes payable									$ 435,900,000
Notes payable Member
Principal outstanding repayable
Notes payable										$ 878,700,000
Interest rate, minimum (as a percent)										2.60%
Interest rate, maximum (as a percent)										5.50%
Notes payable Member | Minimum
Principal outstanding repayable
Maturity term										2 years
Notes payable Member | Maximum
Principal outstanding repayable
Maturity term										8 years 7 months 6 days
Revolving credit facility
Long Term Debt
Maximum borrowing capacity under credit facility					$ 700,000,000
Principal outstanding repayable
Leverage ratio			4.46								4.46
Remaining borrowing capacity available			$ 270,000,000							$ 151,000,000	$ 270,000,000
Debt issuance costs					4,900,000
Maximum borrowing capacity under credit facility before amendment					$ 450,000,000
Extended maturity term					5 years
Revolving credit facility | One-month LIBOR
Long Term Debt
Variable rate of debt			one-month LIBOR
Basis spread on variable rate (as a percent)			2.75%
Revolving credit facility | WEST
Principal outstanding repayable
Number of engines pledged as collateral | engine									22
Revolving credit facility | Credit agreement | Minimum
Principal outstanding repayable
Interest coverage ratio										2.25
Revolving credit facility | Credit agreement | Maximum
Principal outstanding repayable
Leverage ratio										5.00
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										$ 700,000,000
Notes payable			$ 430,000,000							549,000,000	430,000,000
Principal outstanding repayable
Notes payable			430,000,000							$ 549,000,000	$ 430,000,000
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%	2.75%
Term notes | WOLF
Long Term Debt
Notes payable			24,000,000								$ 24,000,000
Principal outstanding repayable
Notes payable			$ 24,000,000								$ 24,000,000
Face amount							$ 36,000,000
Loan Paid off		$ 23,100,000
Discount (in percentage)		5.00%
Number of term notes held | item			2								2