Investments (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended	1 Months Ended	6 Months Ended	12 Months Ended		30 Months Ended			1 Months Ended	6 Months Ended			1 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2011 WMES item	Jun. 30, 2013 WMES item	Dec. 31, 2012 WMES	Dec. 31, 2011 WMES	Jun. 30, 2013 WMES item	May 25, 2011 WMES	Jun. 30, 2013 WMES JA Mitsui Leasing, Ltd	Dec. 31, 2005 WOLF item	Jun. 30, 2013 WOLF item	Jun. 28, 2013 WOLF	Dec. 31, 2012 WOLF	May 31, 2013 WOLF Term notes item	May 31, 2013 WOLF Amended term notes item	Jun. 30, 2013 WOLF Amended term notes	Jun. 30, 2013 WOLF Minimum	Jun. 30, 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
Reference rate, description			one-month LIBOR		one-month LIBOR									one-month LIBOR					one-month LIBOR
Margin (as a percent)																			4.00%	1.00%	2.50%
Maturity term							7 years
Maintenance reserve revenue	11,788,000	9,437,000	21,017,000	18,015,000										9,000,000
Investment in joint venture	31,451,000		31,451,000		21,831,000		17,714,000	11,766,000		17,714,000				13,737,000		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					$ 36,000,000
Number of term notes paid off																	2
Number of term notes amended																		2
Remaining membership interest to be purchased (as a percent)															50.00%