Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Common Stock	Capital Surplus	Retained Earnings Cumulative effect adjustment	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Cumulative effect adjustment	Total
Balance (ASC 842) at May. 31, 2019			$ 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				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 (ASC 842) at May. 31, 2019			$ 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								20.9
Other comprehensive income, net of tax								1.0
Balance at Feb. 29, 2020	45.3	481.5		725.1	(282.6)	(39.9)		929.4
Balance at Aug. 31, 2019	45.3	476.0		713.8	(284.8)	(40.8)		909.5
Increase (Decrease) in Stockholders' Equity
Net income				14.2				14.2
Cash dividends				(2.6)				(2.6)
Stock option activity		0.9			1.2			2.1
Restricted stock activity		1.8						1.8
Repurchase of shares					(4.1)			(4.1)
Other comprehensive income, net of tax						0.8		0.8
Balance at Nov. 30, 2019	45.3	478.7		725.4	(287.7)	(40.0)		921.7
Increase (Decrease) in Stockholders' Equity
Net income				2.3				2.3
Cash dividends				(2.6)				(2.6)
Stock option activity		0.5			5.3			5.8
Restricted stock activity		2.3			(0.2)			2.1
Other comprehensive income, net of tax						0.1		0.1
Balance at Feb. 29, 2020	45.3	481.5		725.1	(282.6)	(39.9)		929.4
Balance at May. 31, 2020	45.3	478.6		706.0	(282.7)	(44.6)		902.6
Increase (Decrease) in Stockholders' Equity
Net income				(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
Balance at May. 31, 2020	45.3	478.6		706.0	(282.7)	(44.6)		902.6
Increase (Decrease) in Stockholders' Equity
Net income								21.8
Other comprehensive income, net of tax								2.2
Balance at Feb. 28, 2021	45.3	477.4		727.7	(275.6)	(42.4)		932.4
Balance at Aug. 31, 2020	45.3	473.1		691.4	(276.1)	(43.1)		890.6
Increase (Decrease) in Stockholders' Equity
Net income				8.2				8.2
Stock option activity		1.1			0.1			1.2
Restricted stock activity		0.9			(0.3)			0.6
Other comprehensive income, net of tax						0.1		0.1
Balance at Nov. 30, 2020	45.3	475.1		699.6	(276.3)	(43.0)		900.7
Increase (Decrease) in Stockholders' Equity
Net income				28.1				28.1
Stock option activity		1.0			0.9			1.9
Restricted stock activity		1.3			(0.2)			1.1
Other comprehensive income, net of tax						0.6		0.6
Balance at Feb. 28, 2021	$ 45.3	$ 477.4		$ 727.7	$ (275.6)	$ (42.4)		$ 932.4