Fair Value Measurements (Details) - USD ($) $ in Millions		3 Months Ended
		Aug. 31, 2014	Aug. 31, 2015
Assets:
Investment in noncontrolling affiliate	[1]	$ 0.0	$ 8.0
Carrying Value
Assets:
Investment in noncontrolling affiliate		0.0	8.0
Fair Value
Assets:
Investment in noncontrolling affiliate		0.0	8.0
Senior unsecured public notes, net of unamortized discount and deferred costs | Carrying Value
Liabilities:
Carrying and estimated fair value of financial instruments		347.9	348.4
Senior unsecured public notes, net of unamortized discount and deferred costs | Fair Value
Liabilities:
Carrying and estimated fair value of financial instruments		391.2	386.4
Industrial revenue bond | Carrying Value
Liabilities:
Carrying and estimated fair value of financial instruments		4.0	4.0
Industrial revenue bond | Fair Value
Liabilities:
Carrying and estimated fair value of financial instruments		4.0	4.0
Fair value measured on recurring basis
Assets:
Cash and cash equivalents		552.5	756.8
Other		0.6	0.5
Liabilities:
Other		12.2	1.0
Fair value measured on recurring basis | Level 1
Assets:
Cash and cash equivalents		552.5	756.8
Other		0.6	0.5
Liabilities:
Other		0.6	0.5
Fair value measured on recurring basis | Level 2
Assets:
Cash and cash equivalents		0.0	0.0
Other		0.0	0.0
Liabilities:
Other		0.0	0.0
Fair value measured on recurring basis | Level 3
Assets:
Cash and cash equivalents		0.0	0.0
Other		0.0	0.0
Liabilities:
Other		11.6	$ 0.5
Decrease due to payments		11.6
Decrease due to currency rate fluctuations		1.6
Fair value measured on recurring basis | Level 3 | Selling, Distribution, and Administrative Expenses
Liabilities:
Increase in estimated fair value		$ 2.1

[1] The Company holds an equity investment in an unconsolidated affiliate. This strategic investment represents less than a 20% ownership interest in the privately-held affiliate, and the Company does not maintain power over or control of the entity. The Company accounts for this investment using the cost method.