STOCKHOLDERS' EQUITY - Changes in AOCI (Details) $ in Millions	12 Months Ended
	May 31, 2020 USD ($)
Changes in AOCI:
Balance at the beginning of the period	$ (4.6)
Balance at the end of the period	240.0
Accumulated Other Comprehensive Loss
Changes in AOCI:
Balance at the beginning of the period	(25.3)
Other comprehensive income before reclassifications, net of tax	(15.7)
Amounts reclassified out of AOCI, net of tax	0.5
Net current-period other comprehensive income (loss)	(15.2)
Balance at the end of the period	(40.5)
Foreign Currency Translation Gains (Losses)
Changes in AOCI:
Balance at the beginning of the period	(20.3)
Other comprehensive income before reclassifications, net of tax	(16.0)
Net current-period other comprehensive income (loss)	(16.0)
Balance at the end of the period	(36.3)
Pension and Post-Retirement Benefits
Changes in AOCI:
Balance at the beginning of the period	(5.0)
Other comprehensive income before reclassifications, net of tax	0.3
Amounts reclassified out of AOCI, net of tax	0.5
Net current-period other comprehensive income (loss)	0.8
Balance at the end of the period	$ (4.2)