Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Total
Increase (Decrease) in Stockholders' Equity
Cumulative effect adjustment upon adoption of ASC 842 on June 1, 2019 | ASC 842			$ 2.5			$ 2.5
Balance at May. 31, 2019	$ 45.3	$ 479.4	709.8	$ (287.7)	$ (40.9)	905.9
Increase (Decrease) in Stockholders' Equity
Net income (loss)			4.4			4.4
Cash dividends			(2.9)			(2.9)
Stock option activity		0.9		1.8		2.7
Restricted stock activity		(4.3)		1.1		(3.2)
Other comprehensive income, net of tax					0.1	0.1
Balance at Aug. 31, 2019	45.3	476.0	713.8	(284.8)	(40.8)	909.5
Balance at May. 31, 2020	45.3	478.6	706.0	(282.7)	(44.6)	902.6
Increase (Decrease) in Stockholders' Equity
Net income (loss)			(14.5)			(14.5)
Cash dividends			(0.1)			(0.1)
Stock option activity		0.5		0.5		1.0
Restricted stock activity		(6.0)		6.1		0.1
Other comprehensive income, net of tax					1.5	1.5
Balance at Aug. 31, 2020	$ 45.3	$ 473.1	$ 691.4	$ (276.1)	$ (43.1)	$ 890.6