Financing Arrangements (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended											3 Months Ended		9 Months Ended			0 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	May 31, 2013	Feb. 28, 2014 Revolving credit facility expiring April 24, 2018 with interest payable monthly	May 31, 2013 Revolving credit facility expiring April 24, 2018 with interest payable monthly	Feb. 28, 2014 Secured credit facility (secured by aircraft and related engines and components) due April 23, 2015 with floating interest rate, payable monthly	May 31, 2013 Secured credit facility (secured by aircraft and related engines and components) due April 23, 2015 with floating interest rate, payable monthly	Feb. 28, 2014 Note payable due March 9, 2017 with floating interest rate, payable semi-annually on June 1 and December 1	May 31, 2013 Note payable due March 9, 2017 with floating interest rate, payable semi-annually on June 1 and December 1	Feb. 28, 2014 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15	May 31, 2013 Notes payable due January 15, 2022 with interest at 7.25% payable semi-annually on January 15 and July 15	Feb. 28, 2014 Convertible notes payable	Feb. 28, 2013 Convertible notes payable	Feb. 28, 2014 Convertible notes payable	Feb. 28, 2013 Convertible notes payable	May 31, 2013 Convertible notes payable	Mar. 03, 2014 Convertible notes payable due March 1, 2014 with interest at 1.625% payable semi-annually on March 1 and September 1	Feb. 28, 2014 Convertible notes payable due March 1, 2014 with interest at 1.625% payable semi-annually on March 1 and September 1	May 31, 2013 Convertible notes payable due March 1, 2014 with interest at 1.625% payable semi-annually on March 1 and September 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	Feb. 28, 2014 Convertible notes payable due February 1, 2015 with interest at 1.75% payable semi-annually on February 1 and August 1	May 31, 2013 Convertible notes payable due February 1, 2015 with interest at 1.75% payable semi-annually on February 1 and August 1	Feb. 28, 2014 Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 1	May 31, 2013 Convertible notes payable due March 1, 2016 with interest at 2.25% payable semi-annually on March 1 and September 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	Feb. 28, 2014 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	Feb. 28, 2014 7.25% bonds, 1.625% and 2.25% convertible notes	Feb. 28, 2014 7.25% bonds, 1.625% and 2.25% convertible notes Level 2	Feb. 28, 2014 Remaining variable rate and fixed rate debt Level 3	Feb. 28, 2014 Note payable due March 15, 2014	May 31, 2013 Note payable due March 15, 2014	Feb. 28, 2014 Mortgage loan (secured by Wood Dale, Illinois facility) due August 1, 2015 with interest at 5.01%	May 31, 2013 Mortgage loan (secured by Wood Dale, Illinois facility) due August 1, 2015 with interest at 5.01%	Feb. 28, 2014 Industrial revenue bond (secured by property, plant and equipment) due August 1, 2018	May 31, 2013 Industrial revenue bond (secured by property, plant and equipment) due August 1, 2018	Feb. 28, 2014 Other	May 31, 2013 Other
Financing Arrangements
Interest rate (as a percent)										7.25%								1.625%		1.625%			2.25%		2.25%		1.75%
Total debt	$ 714.4		$ 708.6	$ 140.0	$ 120.0	$ 32.3	$ 39.2	$ 30.0	$ 40.0	$ 332.8	$ 333.4							$ 68.4	$ 65.9				$ 45.1	$ 43.5													$ 65.8	$ 66.6
Current maturities of debt	(87.8)		(86.4)
Long-term debt	626.6		622.2
Retirement of Principal Amount																	68.4
Amount of convertible notes repurchased																				6.4					5.5		11.0
Cash paid for convertible notes repurchased																				6.1					4.9		11.0
Loss on extinguishment of debt		0.3
Carrying value of long-term debt												148.3		148.3		148.3												443.3
Estimated fair value of long-term debt																													471.4	268.4
Long-term debt:
Principal amount												148.3		148.3		148.3												443.3
Unamortized discount												(5.1)		(5.1)		(9.5)
Net carrying amount												143.2		143.2		138.8					29.7	29.4									0.1	1.2	11.0	11.0	25.0	25.0
Equity component, net of tax												75.3		75.3		75.3
Effective interest rate (as a Percent)																		6.82%					7.41%			5.00%
Interest expense
Coupon interest												0.8	0.8	2.5	2.8
Amortization of deferred financing fees												0.1	0.1	0.3	0.4
Amortization of discount	4.6	8.1										1.5	2.3	4.4	7.9
Interest expense related to convertible notes												$ 2.4	$ 3.2	$ 7.2	$ 11.1