Long Term Debt (Details) (USD $)	3 Months Ended		12 Months Ended	3 Months Ended	0 Months Ended	3 Months Ended				12 Months Ended	0 Months Ended			0 Months Ended			0 Months Ended			3 Months Ended			0 Months Ended	3 Months Ended	12 Months Ended		0 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 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	Mar. 31, 2013 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	Mar. 31, 2013 WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines WEST II Minimum	Sep. 17, 2012 Prior WEST notes	Dec. 31, 2012 Prior WEST notes Interest rate contracts Cash Flow Hedging	Sep. 28, 2012 Note payable at a fixed interest rate of 5.50%, maturing in September 2017. Secured by one engine. item	Mar. 31, 2013 Note payable at a fixed interest rate of 5.50%, maturing in September 2017. Secured by one engine.	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	Mar. 31, 2013 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	Jan. 11, 2010 Note payable at a fixed interest rate of 4.50%, maturing in January 2014. Secured by engines. item	Mar. 31, 2013 Note payable at a fixed interest rate of 4.50%, maturing in January 2014. Secured by engines.	Dec. 31, 2012 Note payable at a fixed interest rate of 4.50%, maturing in January 2014. Secured by engines.	Mar. 31, 2013 Notes payable	Mar. 31, 2013 Notes payable Minimum	Mar. 31, 2013 Notes payable Maximum	Nov. 18, 2011 Revolving credit facility	Mar. 31, 2013 Revolving credit facility	Dec. 31, 2012 Revolving credit facility	Sep. 07, 2012 Revolving credit facility	Sep. 17, 2012 Revolving credit facility WEST item	Mar. 31, 2013 Revolving credit facility Credit agreement	Mar. 31, 2013 Revolving credit facility Credit agreement Minimum	Mar. 31, 2013 Revolving credit facility Credit agreement Maximum
Long Term Debt
Notes payable, net of discount	$ 757,135,000		$ 696,988,000																	$ 757,100,000
Maturity term						10 years					5 years			3 years			4 years				1 year	10 years
Interest rate, minimum (as a percent)																				3.00%
Interest rate, maximum (as a percent)																				5.50%
Maximum borrowing capacity under credit facility																								430,000,000		430,000,000
Remaining borrowing capacity available																								83,000,000	148,000,000
Debt issuance costs																							3,300,000
Maximum borrowing capacity under credit facility before amendment																										345,000,000
Debt to equity ratio			3.20
Variable rate of debt	one-month LIBOR	one-month LIBOR																						one-month LIBOR	LIBOR
Basis spread on variable rate (as a percent)																								2.75%
Aggregate principal amount issued and sold					390,000,000
Net proceeds received from notes issued and sold	69,000,000	20,000,000			384,900,000
Total notes payable before discount	757,135,000					382,800,000	386,700,000		435,900,000			8,500,000	8,600,000		2,000,000	2,300,000		16,900,000	17,300,000
Number of engines pledged as collateral											1						3										22
Number of engines in portfolio offered as collateral				79
Fixed amortization of notes payable						0
Number of business days to pay interest						5 days
Fixed rate (as a percent)						5.50%						5.50%			3.94%			4.50%
Loss on extinguishment of debt and derivative instruments										15,500,000
Period of time over which maintenance obligations are projected						6 months
Minimum amount of cash from maintenance reserve payments required to be held in restricted cash account								9,000,000
Face amount											8,700,000			4,000,000			22,000,000
Interest coverage ratio																													0.0225
Leverage ratio																														0.0450
Minimum consolidated tangible net worth																												183,300,000
Variable rate (as a percent)	0.20%	0.24%
Aggregate maturities
2013	14,521,000
2014	36,023,000
2015	20,934,000
2016 (includes $347.0 million outstanding on revolving credit facility)	369,215,000
2017	29,373,000
Thereafter	287,069,000
Notes payable	757,135,000					382,800,000	386,700,000		435,900,000			8,500,000	8,600,000		2,000,000	2,300,000		16,900,000	17,300,000
Line of credit facility outstanding amount	$ 347,000,000