Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Total
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)	0.0	0.0	(14.5)	0.0	0.0	(14.5)
Cash dividends	0.0	0.0	(0.1)	0.0	0.0	(0.1)
Stock option activity	0.0	0.5	0.0	0.5	0.0	1.0
Restricted stock activity	0.0	(6.0)	0.0	6.1	0.0	0.1
Other comprehensive income (loss), net of tax	0.0	0.0	0.0	0.0	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 (loss)						21.8
Other comprehensive income (loss), 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 (loss)	0.0	0.0	8.2	0.0	0.0	8.2
Stock option activity	0.0	1.1	0.0	0.1	0.0	1.2
Restricted stock activity	0.0	0.9	0.0	(0.3)	0.0	0.6
Other comprehensive income (loss), net of tax	0.0	0.0	0.0	0.0	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 (loss)	0.0	0.0	28.1	0.0	0.0	28.1
Stock option activity	0.0	1.0	0.0	0.9	0.0	1.9
Restricted stock activity	0.0	1.3	0.0	(0.2)	0.0	1.1
Other comprehensive income (loss), net of tax	0.0	0.0	0.0	0.0	0.6	0.6
Balance at Feb. 28, 2021	45.3	477.4	727.7	(275.6)	(42.4)	932.4
Balance at May. 31, 2021	45.3	479.8	741.7	(274.1)	(18.3)	974.4
Increase (Decrease) in Stockholders' Equity
Net income (loss)	0.0	0.0	11.5	0.0	0.0	11.5
Stock option activity	0.0	1.1	0.0	0.2	0.0	1.3
Restricted stock activity	0.0	(1.0)	0.0	2.3	0.0	1.3
Other comprehensive income (loss), net of tax	0.0	0.0	0.0	0.0	(0.3)	(0.3)
Balance at Aug. 31, 2021	45.3	479.9	753.2	(271.6)	(18.6)	988.2
Balance at May. 31, 2021	45.3	479.8	741.7	(274.1)	(18.3)	974.4
Increase (Decrease) in Stockholders' Equity
Net income (loss)						54.8
Other comprehensive income (loss), net of tax						(1.8)
Balance at Feb. 28, 2022	45.3	481.4	796.5	(285.4)	(20.1)	1,017.7
Balance at Aug. 31, 2021	45.3	479.9	753.2	(271.6)	(18.6)	988.2
Increase (Decrease) in Stockholders' Equity
Net income (loss)	0.0	0.0	20.8	0.0	0.0	20.8
Stock option activity	0.0	0.9	0.0	0.0	0.0	0.9
Restricted stock activity	0.0	0.7	0.0	0.0	0.0	0.7
Other comprehensive income (loss), net of tax	0.0	0.0	0.0	0.0	(3.6)	(3.6)
Balance at Nov. 30, 2021	45.3	481.5	774.0	(271.6)	(22.2)	1,007.0
Increase (Decrease) in Stockholders' Equity
Net income (loss)	0.0	0.0	22.5	0.0	0.0	22.5
Stock option activity	0.0	(0.4)	0.0	6.4	0.0	6.0
Restricted stock activity	0.0	0.3	0.0	0.0	0.0	0.3
Repurchase of shares	0.0	0.0	0.0	(20.2)	0.0	(20.2)
Other comprehensive income (loss), net of tax	0.0	0.0	0.0	0.0	2.1	2.1
Balance at Feb. 28, 2022	$ 45.3	$ 481.4	$ 796.5	$ (285.4)	$ (20.1)	$ 1,017.7