Consolidated Statement of Changes in Stockholders’ Equity (USD $) In Millions, except Share data	Total	Class A Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Treasury Stock At Cost [Member]
Balance at May. 31, 2011	$ 740.0	$ 0	$ 0.4	$ 576.6	$ (53.9)	$ 635.8	$ (418.9)
Balance (in Shares) at May. 31, 2011		1,656,200	29,316,691
Net Income (loss)	102.4					102.4
Foreign currency translation adjustment	(8.2)				(8.2)
Pension and postretirement adjustments, net of tax	(12.1)				(12.1)
Stock-based compensation	12.2			12.2
Proceeds from issuance of common stock pursuant to stock-based compensation plans	22.4			22.4
Proceeds from issuance of common stock pursuant to stock-based compensation (in Shares)			724,613
Purchases of treasury stock at cost	(13.1)						(13.1)
Purchases of treasury stock at cost (in Shares)			(475,672)
Treasury stock issued pursuant to stock purchase plans	1.0			(28.2)			29.2
Treasury stock issued pursuant to stock purchase plans (in Shares)			230,279
Dividends	(14.3)					(14.3)
Balance at May. 31, 2012	830.3	0	0.4	583.0	(74.2)	723.9	(402.8)
Balance (in Shares) at May. 31, 2012		1,656,200	29,795,911
Net Income (loss)	31.1					31.1
Foreign currency translation adjustment	(2.6)				(2.6)
Pension and postretirement adjustments, net of tax	11.4				11.4
Stock-based compensation	7.3			7.3
Proceeds from issuance of common stock pursuant to stock-based compensation plans	14.7			14.7
Proceeds from issuance of common stock pursuant to stock-based compensation (in Shares)			507,197
Purchases of treasury stock at cost	(11.8)						(11.8)
Purchases of treasury stock at cost (in Shares)			(432,330)
Treasury stock issued pursuant to stock purchase plans	0.1			(22.1)			22.2
Treasury stock issued pursuant to stock purchase plans (in Shares)			234,701
Dividends	(16.1)					(16.1)
Balance at May. 31, 2013	864.4	0	0.4	582.9	(65.4)	738.9	(392.4)
Balance (in Shares) at May. 31, 2013		1,656,200	30,105,479
Net Income (loss)	44.4					44.4
Foreign currency translation adjustment	(3.1)				(3.1)
Pension and postretirement adjustments, net of tax	13.3				13.3
Stock-based compensation	9.3			9.3
Proceeds from issuance of common stock pursuant to stock-based compensation plans	12.9			12.9
Proceeds from issuance of common stock pursuant to stock-based compensation (in Shares)			473,827
Purchases of treasury stock at cost	(6.2)						(6.2)
Purchases of treasury stock at cost (in Shares)	(200,000)		(215,484)
Treasury stock issued pursuant to stock purchase plans	(1.4)			(24.3)			22.9
Treasury stock issued pursuant to stock purchase plans (in Shares)			242,156
Dividends	(18.2)					(18.2)
Balance at May. 31, 2014	$ 915.4	$ 0	$ 0.4	$ 580.8	$ (55.2)	$ 765.1	$ (375.7)
Balance (in Shares) at May. 31, 2014		1,656,200	30,605,978