Investments (Details) (USD $)	12 Months Ended					18 Months Ended			12 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 WMES item	Dec. 31, 2011 WMES	Dec. 31, 2012 WMES item	May 25, 2011 WMES	Dec. 31, 2012 WMES JA Mitsui Leasing, Ltd	Dec. 31, 2012 WMES BOT Lease Co., Ltd.	Dec. 31, 2005 WOLF item	Dec. 31, 2012 WOLF	Dec. 31, 2011 WOLF	Dec. 31, 2010 WOLF	Dec. 31, 2012 WOLF Minimum	Dec. 31, 2012 WOLF Maximum
Investments
Ownership interest (as a percent)	50.00%			50.00%		50.00%					50.00%
Initial capital contribution							$ 8,000,000
Additional capital contributions				5,600,000	1,000,000
Number of engines transfer to joint venture				7
Number of engines purchased						8
Number of engines in lease portfolio				15
Capital contributions to date				14,600,000		14,600,000
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				11,000,000		11,000,000
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	1,759,000	1,295,000	1,109,000	755,000	3,000						1,004,000	1,292,000
Reference rate, description											one-month LIBOR
Margin (as a percent)														1.00%	2.50%
Maturity term									7 years
Investment in joint venture	21,831,000	15,239,000	9,381,000	11,766,000	5,376,000	11,766,000					10,065,000	9,863,000	9,381,000
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