Investments (Details) (USD $)	3 Months Ended			3 Months Ended	12 Months Ended		21 Months Ended			3 Months Ended	1 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 WMES item	Dec. 31, 2012 WMES	Dec. 31, 2011 WMES	Mar. 31, 2013 WMES item	May 25, 2011 WMES	Mar. 31, 2013 WMES JA Mitsui Leasing, Ltd	Mar. 31, 2013 WMES BOT Lease Co., Ltd.	Dec. 31, 2005 WOLF item	Mar. 31, 2013 WOLF item	Dec. 31, 2012 WOLF	Mar. 31, 2013 WOLF Minimum	Mar. 31, 2013 WOLF Maximum
Investments
Ownership interest (as a percent)				50.00%			50.00%					50.00%
Initial capital contribution								$ 8,000,000
Additional capital contributions				6,100,000	5,600,000	1,000,000
Number of engines transfer to joint venture				7
Number of engines purchased							16
Number of engines in lease portfolio				23								8
Capital contributions to date				20,700,000			20,700,000
Proportionate gain on sale of engines to joint venture interest which is off-set against investments				3,600,000
Net investment after deducting partial offset				17,100,000			17,100,000
Gain on sale of engines				7,200,000
Credit facility established by equity method investee				8,000,000			8,000,000		180,000,000
Earnings from joint ventures	93,000	397,000		(182,000)								275,000
Reference rate, description	one-month LIBOR	one-month LIBOR										one-month LIBOR
Margin (as a percent)														1.00%	2.50%
Maturity term										7 years		4 years
Investment in joint venture	28,070,000		21,831,000	17,730,000	11,766,000		17,730,000					10,340,000	10,065,000
Number of Airbus A340-313 aircraft purchased											2
Purchase price of aircraft											96,000,000
Number of term notes held											4
Number of financial institutions associated with funding of term notes											1
Loan for purchase of aircraft											$ 76,800,000