Long Term Debt (Details) (USD $)	3 Months Ended	6 Months Ended		12 Months Ended	0 Months Ended	6 Months Ended				0 Months Ended	6 Months Ended		0 Months Ended			0 Months Ended	6 Months Ended		6 Months Ended			0 Months Ended	6 Months Ended			0 Months Ended
	Mar. 31, 2013	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	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	Jun. 30, 2013 WEST II Series 2012-A term notes payable at a fixed rate of interest maturing in September 2037. Secured by engines WEST II item	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	Jun. 30, 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	Sep. 28, 2012 Note payable at a fixed interest rate of 5.50%, maturing in September 2017. Secured by one engine.	Jun. 30, 2013 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	Jun. 30, 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.	Jun. 30, 2013 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.	Jun. 30, 2013 Notes payable	Jun. 30, 2013 Notes payable Minimum	Jun. 30, 2013 Notes payable Maximum	Nov. 18, 2011 Revolving credit facility	Jun. 30, 2013 Revolving credit facility	Jun. 18, 2013 Revolving credit facility	Dec. 31, 2012 Revolving credit facility	Sep. 17, 2012 Revolving credit facility WEST item	Jun. 30, 2013 Revolving credit facility Credit agreement	Jun. 30, 2013 Revolving credit facility Credit agreement Minimum	Jun. 30, 2013 Revolving credit facility Credit agreement Maximum
Long Term Debt
Notes payable		$ 744,498,000		$ 696,988,000															$ 744,500,000
Maturity term						10 years				5 years			3 years			4 years				7 months	9 years
Interest rate, minimum (as a percent)																			3.40%
Interest rate, maximum (as a percent)																			5.50%
Maximum borrowing capacity under credit facility																							450,000,000	450,000,000
Remaining borrowing capacity available																							111,000,000		148,000,000
Debt issuance costs																						3,300,000
Maximum borrowing capacity under credit facility before amendment																								430,000,000
Debt to equity ratio	4.30
Variable rate of debt		one-month LIBOR		one-month LIBOR																			LIBOR
Basis spread on variable rate (as a percent)																							3.25%
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		744,498,000				378,900,000	386,700,000		435,900,000		8,400,000	8,600,000		1,700,000	2,300,000		16,500,000	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%
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																												2.50
Leverage ratio																													4.75
Minimum consolidated tangible net worth																											190,600,000
One-month LIBOR rate (as a percent)		0.19%	0.25%
Aggregate maturities
2013		9,883,000
2014		36,023,000
2015		20,934,000
2016 (includes $339.0 million outstanding on revolving credit facility)		361,216,000
2017		29,373,000
Thereafter		287,069,000
Notes payable		744,498,000				378,900,000	386,700,000		435,900,000		8,400,000	8,600,000		1,700,000	2,300,000		16,500,000	17,300,000
Line of credit facility outstanding amount		$ 339,000,000