Long Term Debt (Details) (USD $)	9 Months Ended			0 Months Ended		3 Months Ended	0 Months Ended	3 Months Ended		9 Months Ended	0 Months Ended		9 Months Ended				1 Months Ended	9 Months Ended		0 Months Ended				0 Months Ended	1 Months Ended		1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 17, 2012 Interest Rate Contract [Member] Cash Flow Hedging [Member]	Sep. 17, 2012 Prior WEST notes	Sep. 30, 2012 Prior WEST notes	Sep. 17, 2012 Prior WEST notes Interest Rate Contract [Member] Cash Flow Hedging [Member]	Sep. 30, 2012 Prior WEST notes Interest Rate Contract [Member] Cash Flow Hedging [Member]	Sep. 30, 2012 5.50% five year term loan	Sep. 30, 2012 WEST II item	Sep. 17, 2012 WEST II Notes	Sep. 30, 2012 WEST II Notes	Sep. 30, 2012 WEST II 5.50% five year term loan	Sep. 30, 2012 Notes payable	Sep. 30, 2012 Notes payable Minimum	Sep. 30, 2012 Notes payable Maximum	Nov. 30, 2011 Revolving credit facility	Sep. 30, 2012 Revolving credit facility	Sep. 07, 2012 Revolving credit facility	Sep. 17, 2012 Revolving credit facility WEST II item	Sep. 30, 2012 Revolving credit facility Credit agreement	Sep. 30, 2012 Revolving credit facility Minimum Credit agreement	Sep. 30, 2012 Revolving credit facility Maximum Credit agreement	Sep. 28, 2012 Term loan 5.50% five year term loan item	Sep. 30, 2011 Term loan 3.94% three year term loan	Sep. 30, 2012 Term loan 3.94% three year term loan	Jan. 31, 2010 Term loan 4.50% four year term loan item	Sep. 30, 2012 Term loan 4.50% four year term loan	Jan. 11, 2010 Term loan 4.50% four year term loan
Long Term Debt
Notes payable, net of discount	$ 690,041,000		$ 718,134,000											$ 690,000,000
Maturity term															15 months	10 years									3 years		4 years
Interest rate, minimum (as a percent)														2.71%
Interest rate, maximum (as a percent)														5.50%
Maximum borrowing capacity under credit facility																		430,000,000
Funds available																		159,000,000
Debt issuance costs																	3,300,000
Maximum borrowing capacity under credit facility before amendment																			345,000,000
Debt to equity ratio																		2.82
Variable rate of debt	one-month LIBOR	one-month LIBOR																LIBOR
Basis spread on variable rate (as a percent)																		2.50%
Aggregate principal amount issued and sold											390,000,000
Number of engines in portfolio offered as collateral										79
Number of business days to pay interest													5 days
Loss on extinguishment of debt and derivative instruments								15,400,000
Loss on extinguishment of debt and derivative instruments						15,400,000
Write-off of unamortized debt issuance costs and note discount					5,300,000
Termination of interest rate swaps				10,100,000			10,100,000
Face amount																								8,700,000	4,000,000				22,000,000
Fixed rate (as a percent)									5.50%																3.94%				4.50%
Outstanding loan	690,041,000				435,900,000							390,000,000														2,700,000		17,700,000
Net proceeds received from notes issued and sold	537,693,000	74,410,000									384,900,000
Number of engines pledged as collateral																				22				1			3
Variable rate (as a percent)	0.21%	0.24%
Restricted net assets	54,225,000		76,252,000
Interest coverage ratio																						225.00%
Leverage ratio																							450.00%
Minimum amount of cash from maintenance reserve payments required to be held in restricted cash account												9,000,000
Minimum consolidated tangible net worth																					178,900,000
Aggregate maturities
2012	4,053,000
2013	19,237,000
2014	36,160,000
2015	20,934,000
2016 (includes $271.0 million outstanding on revolving credit facility)	293,216,000
Thereafter	316,441,000
Notes payable	690,041,000				435,900,000							390,000,000														2,700,000		17,700,000
Line of credit facility outstanding amount	$ 271,000,000