Financing Arrangements (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	0 Months Ended	9 Months Ended					9 Months Ended										3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended		9 Months Ended		0 Months Ended	3 Months Ended	9 Months Ended
	Feb. 14, 2013	Feb. 28, 2013	Feb. 29, 2012	May 31, 2012	Feb. 28, 2013 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	Feb. 28, 2013 Note payable due July 19, 2012 with interest at 7.22%, payable monthly	May 31, 2012 Note payable due July 19, 2012 with interest at 7.22%, payable monthly	Feb. 28, 2013 Note payable due March 15, 2014 with floating interest rate, payable monthly	May 31, 2012 Note payable due March 15, 2014 with floating interest rate, payable monthly	Feb. 28, 2013 Note payable due March 9, 2017 with floating interest rate, payable quarterly	May 31, 2012 Note payable due March 9, 2017 with floating interest rate, payable quarterly	Feb. 28, 2013 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	Feb. 28, 2013 Mortgage loan (secured by Wood Dale, Illinois facility) due August 1, 2015 with interest at 5.01%	May 31, 2012 Mortgage loan (secured by Wood Dale, Illinois facility) due August 1, 2015 with interest at 5.01%	Feb. 28, 2013 Convertible notes payable	Feb. 29, 2012 Convertible notes payable	Feb. 28, 2013 Convertible notes payable	Feb. 29, 2012 Convertible notes payable	May 31, 2012 Convertible notes payable	Feb. 28, 2013 Convertible notes payable due February 1, 2026 with interest at 1.75% payable semi-annually on February 1 and August 1	Feb. 28, 2013 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	Feb. 28, 2013 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	Feb. 14, 2013 Convertible notes payable due February 1, 2015 with interest at 1.75% payable semi-annually on February 1 and August 1 item	Feb. 28, 2013 Convertible notes payable due February 1, 2015 with interest at 1.75% payable semi-annually on February 1 and August 1	Feb. 28, 2013 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	Feb. 28, 2013 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 Industrial revenue bond (secured by trust indenture on property, plant and equipment) due August 1, 2018 with floating interest rate, payable monthly	Feb. 28, 2013 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	Feb. 28, 2013 Revolving credit facility subject to annual review in March with interest payable quarterly	May 31, 2012 Revolving credit facility subject to annual review in March with interest payable quarterly
Financing Arrangements
Interest rate (as a percent)								7.22%					7.25%		5.01%							1.75%	1.75%		1.625%			1.75%	2.25%
Total debt		$ 722.8		$ 792.2	$ 305.0	$ 280.0		$ 8.4	$ 1.6	$ 2.6	$ 40.0	$ 50.0	$ 172.2	$ 172.1	$ 11.0	$ 11.0	$ 140.0		$ 140.0		$ 209.5	$ 2.7	$ 2.7	$ 94.9	$ 65.0	$ 68.5		$ 29.3	$ 43.0	$ 46.1	$ 25.0	$ 25.0	$ 27.4	$ 33.0	$ 0.6	$ 0.6
Current maturities of debt		(22.2)		(122.8)
Long-term debt		700.6		669.4
Redemption price of debt instrument as a percentage of the principal amount																						100.00%	100.00%
Amount of convertible notes repurchased																							11.0		6.4				5.5
Cash paid for convertible notes repurchased																						63.6	11.0		6.1				4.9
Aggregate principal amount of securities exchanged	22.7
Loss on extinguishment of debt		0.3
Cash portion received in new debt issuance	7.3
Debt repayment							8.4
Face value of long-term debt		736.5															150.9		150.9		229.3						30.0
Estimated fair value of long-term debt		743.8
Long-term debt:
Principal amount		736.5															150.9		150.9		229.3						30.0
Unamortized discount																	(10.9)		(10.9)		(19.8)
Net carrying amount		722.8		792.2	305.0	280.0		8.4	1.6	2.6	40.0	50.0	172.2	172.1	11.0	11.0	140.0		140.0		209.5	2.7	2.7	94.9	65.0	68.5		29.3	43.0	46.1	25.0	25.0	27.4	33.0	0.6	0.6
Notice period for redemption of debt instrument (in days)																											30
Yield to maturity (as a percent)																											3.75%
Call price at maturity (in dollars per share)																											$ 104.038
Equity component, net of tax																	75.3		75.3		74.8
Effective interest rate (as a percent)																									6.82%			5.00%	7.41%
Interest expense
Coupon interest																	0.8	1.3	2.8	3.7
Amortization of deferred financing fees																	0.1	0.2	0.4	0.6
Amortization of discount		8.1	9.9														2.3	3.3	7.9	9.8
Interest expense related to convertible notes																	$ 3.2	$ 4.8	$ 11.1	$ 14.1