Fair Value Measurements - Financial Instruments on a Recurring Basis (Details) (USD $)	Feb. 28, 2015	May 31, 2014
Fair value on a recurring basis
Marketable securities	$ 44,874,000us-gaap_AvailableForSaleSecurities	$ 0us-gaap_AvailableForSaleSecurities
Fair Value, Measurements, Recurring
Fair value on a recurring basis
Cash and cash equivalents	358,320,000	513,288,000
Total assets at fair value	403,194,000	513,288,000
Current accrued liabilities	286,000	286,000
Total liabilities at fair value	286,000	286,000
Level 1 \| Fair Value, Measurements, Recurring
Fair value on a recurring basis
Cash and cash equivalents	358,320,000	513,288,000
Total assets at fair value	358,320,000	513,288,000
Current accrued liabilities	0	0
Total liabilities at fair value	0	0
Level 2 \| Fair Value, Measurements, Recurring
Fair value on a recurring basis
Cash and cash equivalents	0	0
Total assets at fair value	44,874,000	0
Total liabilities at fair value	286,000	286,000
Level 3 \| Fair Value, Measurements, Recurring
Fair value on a recurring basis
Cash and cash equivalents	0	0
Total assets at fair value	0	0
Current accrued liabilities	0	0
Total liabilities at fair value	0	0
Foreign Exchange Forward \| Level 2 \| Fair Value, Measurements, Recurring
Fair value on a recurring basis
Current accrued liabilities	286,000	286,000
Canadian treasury securities
Fair value on a recurring basis
Marketable securities		0
Canadian treasury securities \| Fair Value, Measurements, Recurring
Fair value on a recurring basis
Marketable securities	44,874,000
Canadian treasury securities \| Level 1 \| Fair Value, Measurements, Recurring
Fair value on a recurring basis
Marketable securities	0
Canadian treasury securities \| Level 2 \| Fair Value, Measurements, Recurring
Fair value on a recurring basis
Marketable securities	44,874,000
Canadian treasury securities \| Level 3 \| Fair Value, Measurements, Recurring
Fair value on a recurring basis
Marketable securities	$ 0

Fair value portion of trade and related party payables and accrued expenses.

No definition available.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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- Definition

Aggregation of the liabilities reported on the balance sheet measured at fair value on a recurring basis by the entity.

+ References

No definition available.

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