Aircraft Portfolio (Details) $ in Millions	12 Months Ended
	May. 31, 2015 USD ($) aircraft item	May. 31, 2014 USD ($)	May. 31, 2013 USD ($) item
Aircraft portfolio
Sales from services	$ 702.9	$ 807.8	$ 907.3
Owned Through Joint Ventures
Aircraft portfolio
Equity investments	20.5	28.7
Investment in joint ventures, receivable from sale of aircraft	$ 5.7	12.2
Membership interest in joint ventures (as a percent)	50.00%
Sales from services	$ 0.1	0.1	0.5
Summarized income statement information
Sales	14.7	10.4	115.2
Income before provision for income taxes	$ 0.9	6.7	$ 13.5
Number of aircraft sold by joint venture partners | item	1		12
Revenue from sale of aircraft by joint venture partners	$ 5.1		$ 77.9
Balance sheet information:
Assets	48.2	71.3
Debt	4.6	11.4
Members' capital	$ 41.0	$ 57.5
Wholly-Owned
Aircraft portfolio
Membership interest in joint ventures (as a percent)	100.00%
Balance sheet information:
Number of aircraft sold | aircraft	2
Aircraft | Owned Through Joint Ventures
Aircraft portfolio
Owned aircraft, number | item	3