Financing Arrangements (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended							9 Months Ended			9 Months Ended										1 Months Ended			3 Months Ended		3 Months Ended						3 Months Ended		9 Months Ended			9 Months Ended		9 Months Ended			9 Months Ended								3 Months Ended
	Feb. 29, 2012	Feb. 28, 2011	May 31, 2011	Feb. 29, 2012 Recourse Debt	Feb. 29, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7)	Oct. 13, 2011 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7)	May 31, 2011 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7)	Feb. 29, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7) Eurodollar rate	Feb. 29, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7) Eurodollar rate Minimum	Feb. 29, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7) Eurodollar rate Maximum	Feb. 29, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7) Base rate	Feb. 29, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7) Base rate Minimum	Feb. 29, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly (see Note 7) Base rate Maximum	Feb. 29, 2012 Note payable due July 19, 2012 with interest at 7.22%, payable monthly	May 31, 2011 Note payable due July 19, 2012 with interest at 7.22%, payable monthly	Feb. 29, 2012 Revolving credit facility (secured by aircraft and related engines and components) due April 23, 2015 with floating interest rate, payable monthly	May 31, 2011 Revolving credit facility (secured by aircraft and related engines and components) due April 23, 2015 with floating interest rate, payable monthly	Feb. 29, 2012 Revolving credit facility expiring March 9, 2012 with interest payable monthly	Feb. 29, 2012 Mortgage loan (secured by Wood Dale, Illinois facility) due August 1, 2015 with interest at 5.01%	May 31, 2011 Mortgage loan (secured by Wood Dale, Illinois facility) due August 1, 2015 with interest at 5.01%	Jan. 31, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 Prior to January 15, 2015	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 Prior to January 15, 2015 Maximum	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 Prior to January 15, 2017	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 On or after January 15, 2017 Minimum D	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 On or after January 15, 2017 Maximum D	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 12-month period beginning on January 15, 2017	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 12-month period beginning on January 15, 2018	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 12-month period beginning on January 15, 2019	Feb. 29, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15 12-month period beginning on January 15, 2020 and thereafter	Feb. 29, 2012 Convertible notes payable	Feb. 28, 2011 Convertible notes payable	Feb. 29, 2012 Convertible notes payable	Feb. 28, 2011 Convertible notes payable	May 31, 2011 Convertible notes payable	Feb. 29, 2012 Convertible notes payable due March 1, 2014 with interest at 1.625% payable semi-annually on March 1 and September 1	May 31, 2011 Convertible notes payable due March 1, 2014 with interest at 1.625% payable semi-annually on March 1 and September 1	Feb. 29, 2012 Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 1	Feb. 28, 2011 Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 1	May 31, 2011 Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 1	Feb. 29, 2012 Convertible notes payable due February 1, 2026 with interest at 1.75% payable semi-annually on February 1 and August 1	May 31, 2011 Convertible notes payable due February 1, 2026 with interest at 1.75% payable semi-annually on February 1 and August 1	Feb. 29, 2012 Industrial revenue bond (secured by trust indenture on property, plant and equipment) due August 1, 2018 with floating interest rate, payable monthly	May 31, 2011 Industrial revenue bond (secured by trust indenture on property, plant and equipment) due August 1, 2018 with floating interest rate, payable monthly	Feb. 29, 2012 Non-recourse note payable due December 8, 2011 with interest at 13.0%	Nov. 30, 2011 Non-recourse note payable due December 8, 2011 with interest at 13.0%	Feb. 29, 2012 Non-recourse note payable due July 19, 2012 with interest at 7.22%	May 31, 2011 Non-recourse note payable due July 19, 2012 with interest at 7.22%	Nov. 30, 2011 Non-recourse note payable due April 3, 2015 with interest at 8.38%	Feb. 29, 2012 Non-recourse note payable due April 3, 2015 with interest at 8.38%	May 31, 2011 Non-recourse note payable due April 3, 2015 with interest at 8.38%
Financing Arrangements
Interest rate (as a percent)														7.22%					5.01%			7.25%															1.625%		2.25%			1.75%				13.00%		7.22%			8.38%
Total recourse debt	$ 820,982		$ 425,304		$ 300,000		$ 100,000							$ 8,907	$ 2,217	$ 60,504	$ 54,940	$ 1,589	$ 11,000	$ 11,000		$ 171,986															$ 76,170	$ 73,418	$ 53,090		$ 51,309	$ 112,736	$ 107,420	$ 25,000	$ 25,000
Current maturities of recourse debt	(221,661)		(111,323)
Long-term recourse debt	599,321		313,981
Total non-recourse debt			11,855																																														8,201			3,654
Current maturities of non-recourse debt			(823)
Long-term non-recourse debt			11,032
Aggregate principal amount of notes sold																					175,000
Debt instrument issuance price as a percentage of the principal amount																					98.268%
Yield to maturity (as a percent)																						7.50%
Percentage of the principal amount of the debt instrument which the entity may redeem with the net cash proceeds from certain equity offerings																								35.00%
Redemption price of debt instrument as a percentage of the principal amount																							107.25%		100.00%			103.625%	102.417%	101.208%	100.00%
Notice period for redemption of debt instrument (in days)																										30	60
Maximum borrowing capacity						580,000
Maximum borrowing capacity under the credit agreement before amendment						400,000
Increase in the revolving commitment subject to the agreement						100,000
Maximum borrowing capacity optional expansion						680,000
Description of variable rate basis								Eurodollar Rate			Base Rate
Basis spread on variable rate (as a percent)									1.25%	2.25%		0.25%	1.25%
Debt associated with aircraft sold, assumed by acquirer																																																		3,252
Non-recourse debt assumed in connection with purchase of joint venture partner's interest in a narrow-body aircraft																																															6,545
Repurchased of convertible notes																																								6,000
Repurchased of convertible notes in cash																																								4,667
Gain on extinguishment of debt		97																																						97
Face value of long-term recourse debt				628,720																												268,380		268,380		268,380
Estimated fair value of long-term recourse debt				627,000
Long-term debt:
Principal amount				628,720																												268,380		268,380		268,380
Unamortized discount																																(26,384)		(26,384)		(36,233)
Net carrying amount																																241,996		241,996		232,147
Equity component, net of tax																																74,966		74,966		74,966
Effective interest rate (as a percent)																																					6.82%		7.41%			8.48%
Interest expense
Coupon interest																																1,229	1,229	3,685	3,704
Amortization of deferred financing fees																																189	189	565	566
Amortization of discount	9,865	9,150																														3,346	3,098	9,848	9,149
Interest expense related to convertible notes																																$ 4,764	$ 4,516	$ 14,098	$ 13,419