Financing Arrangements (Details) (USD $)	12 Months Ended								12 Months Ended			12 Months Ended			12 Months Ended								1 Months Ended				12 Months Ended		12 Months Ended										1 Months Ended			12 Months Ended			1 Months Ended	12 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended						12 Months Ended				3 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010	May 31, 2012 Recourse Debt	May 31, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly	Oct. 13, 2011 Revolving credit facility expiring April 12, 2016 with interest payable monthly	May 31, 2011 Revolving credit facility expiring April 12, 2016 with interest payable monthly	Apr. 12, 2011 Revolving credit facility expiring April 12, 2016 with interest payable monthly	May 31, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly Eurodollar rate	May 31, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly Eurodollar rate Minimum	May 31, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly Eurodollar rate Maximum	May 31, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly Base rate	May 31, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly Base rate Minimum	May 31, 2012 Revolving credit facility expiring April 12, 2016 with interest payable monthly Base rate Maximum	May 31, 2012 Credit Agreement and its Predecessor	May 31, 2011 Credit Agreement and its Predecessor	May 31, 2010 Credit Agreement and its Predecessor	May 31, 2012 Foreign line of credit	May 31, 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	May 31, 2012 Note payable due March 15, 2014 with floating interest rate, payable monthly	May 31, 2012 Note payable due March 9, 2017 with floating interest rate, payable semi-annually on June 1 and December 1	Jan. 31, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15	May 31, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15	Jan. 23, 2012 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15	May 31, 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	May 31, 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	May 31, 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	May 31, 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	May 31, 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	May 31, 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	May 31, 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	May 31, 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	May 31, 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	May 31, 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%	May 31, 2012 Loan Agreement	Mar. 09, 2012 Loan Agreement Y	Mar. 31, 2012 Loan Agreement Eurodollar rate	Mar. 09, 2012 Loan Agreement Eurodollar rate	Mar. 09, 2012 Loan Agreement Telair and Nordisk	May 31, 2012 Convertible notes payable	May 31, 2011 Convertible notes payable	May 31, 2010 Convertible notes payable	Feb. 29, 2008 Convertible notes payable due in 2014 and 2016	May 31, 2012 Convertible notes payable due in 2014 and 2016 D	May 31, 2010 Convertible notes payable due in 2014 and 2016	Feb. 28, 2008 Convertible notes payable due in 2014 and 2016	May 31, 2012 Convertible notes payable due in 2014 and 2016 Minimum Y	May 31, 2012 Convertible notes payable due in 2014 and 2016 Maximum Y	Feb. 29, 2008 Convertible notes payable due March 1, 2014 with interest at 1.625% payable semi-annually on March 1 and September 1	May 31, 2012 Convertible notes payable due March 1, 2014 with interest at 1.625% payable semi-annually on March 1 and September 1	May 31, 2010 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, 2008 Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 1	May 31, 2012 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	May 31, 2010 Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 1	Feb. 28, 2006 Convertible notes payable due February 1, 2026 with interest at 1.75% payable semi-annually on February 1 and August 1	May 31, 2012 Convertible notes payable due February 1, 2026 with interest at 1.75% payable semi-annually on February 1 and August 1 D	May 31, 2011 Convertible notes payable due February 1, 2026 with interest at 1.75% payable semi-annually on February 1 and August 1	May 31, 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	May 31, 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	May 31, 2012 Revolving credit facility (secured by aircraft and related engines and components) due April 23, 2015 with floating interest rate, payable monthly LIBOR	May 31, 2012 Revolving credit facility subject to annual review in March with interest payable quarterly	May 31, 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%	May 31, 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
Maximum borrowing capacity under the credit agreement before amendment								$ 400,000,000
Maximum borrowing capacity						580,000,000												4,370,000																							50,000,000																							65,000,000
Increase in the revolving commitment subject to the agreement						100,000,000
Maximum borrowing capacity optional expansion						680,000,000
Description of variable rate basis									Eurodollar Rate			Base Rate																											Eurodollar Rate																											LIBOR
Basis spread on variable rate (as a percent)										125.00%	225.00%		25.00%	125.00%																										250.00%																										325.00%
Amount outstanding					280,000,000																																50,000,000																											33,022,000	54,940,000
Outstanding letter of credit	16,798,000				14,329,000
Amortization term of debt instrument (in years)																																						5
Interest rate (as a percent)																			7.22%					7.25%											5.01%																	1.625%				2.25%				1.75%								7.22%			8.38%
Total recourse debt	792,184,000	425,304,000			280,000,000		100,000,000												8,380,000	2,217,000	2,590,000	50,000,000		172,039,000											11,000,000	11,000,000																68,493,000		73,418,000		46,119,000	51,309,000			94,913,000	107,420,000	25,000,000	25,000,000	33,022,000	54,940,000		628,000
Current maturities of recourse debt	(122,780,000)	(111,323,000)
Long-term recourse debt	669,404,000	313,981,000
Total non-recourse debt		11,855,000																																																																			8,201,000			3,654,000
Current maturities of non-recourse debt		(823,000)
Long-term non-recourse debt		11,032,000
Aggregate principal amount of notes sold																							175,000,000																						250,000,000						137,500,000				112,500,000				150,000,000
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%																										100.00%
Notice period for redemption of debt instrument (in days)																													30	60
Conversion rate																																														$ 28.6144														$ 34.595
Principal amount of debt used for conversion calculations																																														1,000														1,000
Conversion price (in dollars per share)																																														$ 34.95														$ 28.91
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible																																														20														20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible																																														30														30
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be convertible																																														130.00%														120.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period																																														5														5
Number of consecutive trading days before five consecutive business days during the note measurement period																																														5														5
Percentage of the trading price to the product of the last reported sale price of the entity's common stock and the conversion rate, maximum																																														98.00%														98.00%
Trading day period ending at the close of business on the business day immediately preceding the stated maturity date																																																												10
Amount of cash to be received per $1,000 principal amount upon conversion of the notes, and if less than the conversion value of a number of shares of common stock equal to the conversion rate																																														1,000
Unamortized debt issuance costs																																																4,366,000
Debt issuance costs, amortization period (in years)																																																	6	8
Amount paid for hedges																																													69,676,000
Number or shares available for purchase under the warrants issued																																																7,028,000
Exercise price (in dollars per share)																																																$ 48.83
Amount received from sale of warrants																																													40,114,000
Net proceeds from the notes transaction after paying expenses																																													214,410,000
Net book value of asset held as collateral																																			13,015,000
Retirement/sale of debt																																																				9,421,000	13,110,000			9,100,000	6,000,000	2,000,000		20,551,000										3,252,000
Cash paid for repurchase of notes.																																															11,543,000					8,911,000				8,116,000	4,667,000			20,340,000
(Loss) gain on extinguishment of debt	(664,000)	97,000	893,000																																												893,000					(161,000)				(312,000)	97,000			(191,000)
Short-term borrowing activity
Maximum amount borrowed															525,000,000	135,000,000	150,000,000
Average daily borrowings															288,320,000	70,603,000	40,795,000
Average interest rate during the year (as a percent)															1.90%	1.95%	1.72%
Aggregate par value of recourse debt maturing in next five fiscal years
2013				127,036,000
2014				98,784,000
2015				22,782,000
2016				356,325,000
2017				10,000,000
Face value of long-term recourse debt				814,928,000																																						229,308,000	268,380,000
Estimated fair value of long-term recourse debt				801,289,000
Long-term debt:
Principal amount				814,928,000																																						229,308,000	268,380,000
Unamortized discount																																										(19,783,000)	(36,233,000)
Net carrying amount																																										209,525,000	232,147,000
Equity component, net of tax																																										74,816,000	74,966,000
Effective interest rate (as a percent)																																																				6.82%				7.41%				8.48%
Interest expense
Coupon interest																																										4,866,000	4,932,000	5,102,000
Amortization of deferred financing fees																																										739,000	754,000	775,000
Amortization of discount	13,171,000	12,309,000	11,589,000																																							13,102,000	12,309,000	11,589,000
Interest expense related to convertible notes																																										$ 18,707,000	$ 17,995,000	$ 17,466,000