Notes Payable (Details) (USD $)	12 Months Ended			0 Months Ended		12 Months Ended	0 Months Ended	12 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended			0 Months Ended			0 Months Ended		0 Months Ended			0 Months Ended		12 Months Ended			12 Months Ended		0 Months Ended		12 Months Ended						0 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 17, 2012 Interest rate contracts Cash Flow Hedging	Nov. 18, 2009 Interest rate contracts Cash Flow Hedging	Dec. 31, 2012 WEST II item	Sep. 17, 2012 WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines WEST II	Dec. 31, 2012 WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines WEST II	Dec. 31, 2012 WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines WEST II Minimum	Dec. 31, 2011 WEST Series 2005-A1 term notes payable at a floating rate of interest based on LIBOR plus 1.25%, maturing in July 2018. Secured by engines. Repaid in September 2012	Dec. 31, 2011 WEST Series 2008-A1 term notes payable, a floating rate of interest based on LIBOR plus 1.50%, maturing in March 2021. Secured by engines. Repaid in September 2012	Dec. 31, 2011 WEST Series 2007-A2 warehouse notes payable and Series 2007-B2 warehouse notes payable, secured by engines. Repaid in September 2012	Dec. 31, 2011 WEST Series 2007-A2 warehouse notes payable at a floating rate of interest based on LIBOR plus 2.25%, maturing in January 2024. Secured by engines. Repaid in September 2012	Dec. 31, 2012 WEST Series 2007-A2 warehouse notes payable at a floating rate of interest based on LIBOR plus 2.25%, maturing in January 2024. Secured by engines. Repaid in September 2012	Dec. 31, 2011 WEST Series 2007-B2 warehouse notes payable at LIBOR plus 4.75%, maturing in January 2026. Secured by engines. Repaid in September 2012	Dec. 31, 2012 WEST Series 2007-B2 warehouse notes payable at LIBOR plus 4.75%, maturing in January 2026. Secured by engines. Repaid in September 2012	Dec. 31, 2011 Note payable at a floating rate of LIBOR plus 3.00%. Secured by Series 2005-B1 notes	Dec. 31, 2011 Note payable at a floating rate of LIBOR plus 4.00%. Secured by Series 2008-B1 notes	Dec. 31, 2011 Note payable at a fixed interest rate of 8.00%, unsecured	Jan. 11, 2010 Note payable at a fixed interest rate of 4.50%, maturing in January 2014. Secured by engines. item	Dec. 31, 2012 Note payable at a fixed interest rate of 4.50%, maturing in January 2014. Secured by engines.	Dec. 31, 2011 Note payable at a fixed interest rate of 4.50%, maturing in January 2014. Secured by engines.	Sep. 28, 2012 Note payable at a fixed interest rate of 5.50%, maturing in September 2017. Secured by one engine. item	Dec. 31, 2012 Note payable at a fixed interest rate of 5.50%, maturing in September 2017. Secured by one engine.	Sep. 30, 2011 Note payable at a fixed interest rate of 3.94%, maturing in September 2014. Secured by an aircraft	Dec. 31, 2012 Note payable at a fixed interest rate of 3.94%, maturing in September 2014. Secured by an aircraft	Dec. 31, 2011 Note payable at a fixed interest rate of 3.94%, maturing in September 2014. Secured by an aircraft	Sep. 17, 2012 Prior WEST notes	Sep. 17, 2012 Prior WEST notes Interest rate contracts Cash Flow Hedging	Dec. 31, 2012 Prior WEST notes Interest rate contracts Cash Flow Hedging	Dec. 31, 2012 Notes payable	Dec. 31, 2011 Notes payable	Dec. 31, 2012 Notes payable Minimum	Dec. 31, 2012 Notes payable Maximum	Sep. 30, 2012 Revolving credit facility	Sep. 17, 2012 Revolving credit facility item	Dec. 31, 2012 Revolving credit facility	Sep. 07, 2012 Revolving credit facility	Dec. 31, 2011 Revolving credit facility	Dec. 31, 2012 Revolving credit facility Credit agreement	Dec. 31, 2012 Revolving credit facility Minimum Credit agreement	Dec. 31, 2012 Revolving credit facility Maximum Credit agreement	Nov. 18, 2011 Credit facility at a floating rate of interest of LIBOR plus 2.75%, secured by engines	Dec. 31, 2012 Credit facility at a floating rate of interest of LIBOR plus 2.75%, secured by engines	Dec. 31, 2011 Credit facility at a floating rate of interest of LIBOR plus 2.75%, secured by engines
Long Term Debt
Variable rate of debt										LIBOR	LIBOR		LIBOR		LIBOR		LIBOR	LIBOR																			LIBOR							LIBOR
Basis spread on variable rate (as a percent)										1.25%	1.50%		2.25%		4.75%		3.00%	4.00%																			2.75%							2.75%
Maximum borrowing capacity under credit facility																																					$ 430,000,000	$ 430,000,000	$ 345,000,000					$ 430,000,000	$ 345,000,000
Fixed rate (as a percent)								5.50%											8.00%		4.50%	4.50%		5.50%		3.94%	3.94%
Total notes payable before discount	696,988,000							386,724,000		99,763,000	151,120,000	185,937,000	162,500,000	0	23,500,000	0	16,180,000	15,212,000	1,500,000		17,338,000	18,840,000		8,593,000		2,333,000	3,667,000	435,900,000			696,988,000	720,219,000												282,000,000	228,000,000
Discount on debt instrument	0	(2,085,000)								(3,000)	(2,888)																					(2,085,000)
Notes payable, net of discount	696,988,000	718,134,000																													696,988,000	718,134,000
Variable rate (as a percent)	0.21%	0.30%
Principal outstanding repayable
2013	19,237,000
2014	36,160,000
2015	20,934,000
2016 (includes $282.0 million outstanding on revolving credit facility)	304,215,000
2017	29,373,000
Thereafter	287,069,000
Notes payable	696,988,000							386,724,000		99,763,000	151,120,000	185,937,000	162,500,000	0	23,500,000	0	16,180,000	15,212,000	1,500,000		17,338,000	18,840,000		8,593,000		2,333,000	3,667,000	435,900,000			696,988,000	720,219,000												282,000,000	228,000,000
Interest coverage ratio																																									2.25%
Leverage ratio																																										4.50%
Minimum consolidated tangible net worth																																								182,100,000
Maturity term								10 years												4 years			5 years		3 years								1 year	10 years
Period of time over which maintenance obligations are projected								6 months
Interest rate, minimum (as a percent)																															3.00%
Interest rate, maximum (as a percent)																															5.50%
Remaining borrowing capacity available																																					148,000,000		117,000,000
Debt issuance costs																																											3,300,000
Maximum borrowing capacity under credit facility before amendment																																						345,000,000
Debt to equity ratio																																			3.20
Aggregate principal amount issued and sold							390,000,000
Net proceeds received from notes issued and sold	603,693,000	132,409,000	174,841,000				384,900,000
Number of engines pledged as collateral																				3			1													22
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																														15,500,000
Loss on debt extinguishment	15,462,000	343,000
Write-off of unamortized debt issuance costs and note discount																												5,300,000
Termination of interest rate swaps				10,200,000	(2,600,000)																								10,200,000
Face amount																				22,000,000			8,700,000		4,000,000
Minimum amount of cash from maintenance reserve payments required to be held in restricted cash account	$ 9,000,000								$ 9,000,000