CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Total Equity	Total
Balance at May. 31, 2017	$ 45.2	$ 460.8	$ 727.9	$ (279.8)	$ (39.9)	$ 914.2
Increase (Decrease) in Stockholders' Equity
Net income			15.6			15.6	$ 15.6
Cash dividends			(10.3)			(10.3)
Stock option activity		0.9		11.2		12.1
Restricted stock activity	0.1	8.8		1.0		9.9
Repurchase of shares				(13.1)		(13.1)
Other comprehensive income (loss), net of tax					7.9	7.9	7.9
Balance at May. 31, 2018	45.3	470.5	733.2	(280.7)	(32.0)	936.3
Increase (Decrease) in Stockholders' Equity
Net income			7.5			7.5	7.5
Cash dividends			(10.5)			(10.5)
Stock option activity		3.5		4.1		7.6
Restricted stock activity		5.4		(0.8)		4.6
Repurchase of shares				(10.3)		(10.3)
Other comprehensive income (loss), net of tax					(8.9)	(8.9)	(8.9)
Balance at May. 31, 2019	45.3	479.4	709.8	(287.7)	(40.9)	905.9	905.9
Increase (Decrease) in Stockholders' Equity
Cumulative effect adjustment upon adoption of ASC | ASC 606			(20.4)			(20.4)
Net income			4.4			4.4	4.4
Cash dividends			(10.7)			(10.7)
Stock option activity		3.1		8.3		11.4	8.3
Restricted stock activity		(3.9)		0.8		(3.1)
Repurchase of shares				(4.1)		(4.1)	(4.1)
Other comprehensive income (loss), net of tax					(3.7)	(3.7)	(3.7)
Balance at May. 31, 2020	$ 45.3	$ 478.6	706.0	$ (282.7)	$ (44.6)	902.6	$ 902.6
Increase (Decrease) in Stockholders' Equity
Cumulative effect adjustment upon adoption of ASC | ASC 842			$ 2.5			$ 2.5