Investment Expense (Income), Net - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Investments Debt And Equity Securities [Abstract]
Gross realized gains on sales of available-for-sale securities	$ 0.1		$ 0.3
Gross realized losses on sales of available-for-sale securities	2.2		3.4
Realized gains on trading securities	0.2		0.2
Unrealized losses on trading securities	0.1		0.7
Unrealized gains (losses) on marketable equity securities	$ 3.7		$ (2.9)
Gross gains realized on sales of marketable securities		$ 2.6		$ 8.6
Gross losses realized on sales of marketable securities		$ 0.7		$ 1.8