Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Aug. 31, 2015	May. 31, 2015
Fair value on a recurring basis
Contractual maturities (less than)	1 year	1 year
Canadian treasury securities
Fair value on a recurring basis
Amortized cost basis of marketable securities	$ 53.4	$ 16.1

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant