Financing Arrangements (Details) (USD $)	3 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	May 31, 2012
Financing Arrangements
Total debt	$ 787,600,000		$ 792,200,000
Current maturities of debt	(108,200,000)		(122,800,000)
Long-term debt	679,400,000		669,400,000
Loss on extinguishment of debt	200,000
Face value of long-term debt	806,300,000
Estimated fair value of long-term debt	799,100,000
Long-term debt:
Principal amount	806,300,000
Net carrying amount	787,600,000		792,200,000
Interest expense
Amortization of discount	2,900,000	3,200,000
Revolving credit facility expiring April 12, 2016 with interest payable monthly
Financing Arrangements
Total debt	300,000,000		280,000,000
Long-term debt:
Net carrying amount	300,000,000		280,000,000
Note payable due July 19, 2012 with interest at 7.22%, payable monthly
Financing Arrangements
Interest rate (as a percent)	7.22%
Total debt			8,400,000
Long-term debt:
Net carrying amount			8,400,000
Note payable due March 15, 2014 with floating interest rate, payable monthly
Financing Arrangements
Total debt	2,200,000		2,600,000
Long-term debt:
Net carrying amount	2,200,000		2,600,000
Note payable due March 9, 2017 with floating interest rate, payable semi-annually on June 1 and December 1
Financing Arrangements
Total debt	45,000,000		50,000,000
Long-term debt:
Net carrying amount	45,000,000		50,000,000
Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15
Financing Arrangements
Interest rate (as a percent)	7.25%
Total debt	172,100,000		172,100,000
Long-term debt:
Net carrying amount	172,100,000		172,100,000
Mortgage loan (secured by Wood Dale, Illinois facility) due August 1, 2015 with interest at 5.01%
Financing Arrangements
Interest rate (as a percent)	5.01%
Total debt	11,000,000		11,000,000
Long-term debt:
Net carrying amount	11,000,000		11,000,000
Convertible notes payable
Financing Arrangements
Total debt	200,500,000		209,500,000
Face value of long-term debt	216,300,000		229,300,000
Long-term debt:
Principal amount	216,300,000		229,300,000
Unamortized discount	(15,800,000)		(19,800,000)
Net carrying amount	200,500,000		209,500,000
Equity component, net of tax	74,800,000		74,800,000
Interest expense
Coupon interest	1,000,000	1,200,000
Amortization of deferred financing fees	200,000	200,000
Amortization of discount	2,800,000	3,200,000
Interest expense related to convertible notes	4,000,000	4,600,000
Convertible notes payable due February 1, 2026 with interest at 1.75% payable semi-annually on February 1 and August 1
Financing Arrangements
Interest rate (as a percent)	1.75%
Total debt	88,700,000		94,900,000
Amount of convertible notes repurchased	8,000,000
Cash paid for convertible notes repurchased	7,900,000
Long-term debt:
Net carrying amount	88,700,000		94,900,000
Effective interest rate (as a percent)	8.48%
Convertible notes payable due March 1, 2014 with interest at 1.625% payable semi-annually on March 1 and September 1
Financing Arrangements
Interest rate (as a percent)	1.625%
Total debt	69,400,000		68,500,000
Long-term debt:
Net carrying amount	69,400,000		68,500,000
Effective interest rate (as a percent)	6.82%
Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 1
Financing Arrangements
Interest rate (as a percent)	2.25%
Total debt	42,400,000		46,100,000
Amount of convertible notes repurchased	5,000,000
Cash paid for convertible notes repurchased	4,400,000
Long-term debt:
Net carrying amount	42,400,000		46,100,000
Effective interest rate (as a percent)	7.41%
Industrial revenue bond (secured by trust indenture on property, plant and equipment) due August 1, 2018 with floating interest rate, payable monthly
Financing Arrangements
Total debt	25,000,000		25,000,000
Long-term debt:
Net carrying amount	25,000,000		25,000,000
Revolving credit facility (secured by aircraft and related engines and components) due April 23, 2015 with floating interest rate, payable monthly
Financing Arrangements
Total debt	31,200,000		33,000,000
Long-term debt:
Net carrying amount	31,200,000		33,000,000
Revolving credit facility subject to annual review in March with interest payable quarterly
Financing Arrangements
Total debt	600,000		600,000
Long-term debt:
Net carrying amount	$ 600,000		$ 600,000