Investments - Summary of Company's Investment Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Aug. 31, 2014	May 31, 2014
Summary of Investment Holdings [Line Items]
Available-for-sale, Amortized Cost	$ 25.4	$ 10.4
Available-for-sale, Unrealized Gains	0.1	0.6
Available-for-sale, Unrealized Losses	0	(0.3)
Available-for-sale, Fair Value	25.5	10.7
Trading, Amortized Cost	2.6	1.6
Trading, Realized Gains	0.1	0.3
Trading, Realized Losses	0	(0.1)
Trading, Fair Value	2.7	1.8
Equity securities [Member]
Summary of Investment Holdings [Line Items]
Available-for-sale, Amortized Cost	0.5	0.2
Available-for-sale, Unrealized Gains	0.1	0.6
Available-for-sale, Unrealized Losses	0	(0.3)
Available-for-sale, Fair Value	0.6	0.5
Trading, Amortized Cost	2.6	1.6
Trading, Realized Gains	0.1	0.3
Trading, Realized Losses	0	(0.1)
Trading, Fair Value	2.7	1.8
Time deposit [Member]
Summary of Investment Holdings [Line Items]
Available-for-sale, Amortized Cost	24.9	10.2
Available-for-sale, Unrealized Gains	0	0
Available-for-sale, Unrealized Losses	0	0
Available-for-sale, Fair Value	$ 24.9	$ 10.2