Fair Value Measurements - Schedule of Fair Value of Financial Instruments Measured on a Recurring Basis (Details) - USD ($)	Feb. 28, 2017	May 31, 2016
Fair value on a recurring basis
Marketable securities	$ 0	$ 70,405,000
Fair Value, Measurements, Recurring
Fair value on a recurring basis
Cash and cash equivalents	147,244,000	139,357,000
Interest rate lock agreements	7,346,000
Total assets at fair value	154,590,000	209,762,000
Total liabilities at fair value		19,628,000
Fair Value, Measurements, Recurring \| Interest rate lock agreement
Fair value on a recurring basis
Long term accrued liabilities		19,628,000
Fair Value, Measurements, Recurring \| Canadian treasury securities
Fair value on a recurring basis
Marketable securities		70,405,000
Fair Value, Measurements, Recurring \| Level 1
Fair value on a recurring basis
Cash and cash equivalents	147,244,000	139,357,000
Interest rate lock agreements	0
Total assets at fair value	147,244,000	139,357,000
Total liabilities at fair value		0
Fair Value, Measurements, Recurring \| Level 1 \| Interest rate lock agreement
Fair value on a recurring basis
Long term accrued liabilities		0
Fair Value, Measurements, Recurring \| Level 1 \| Canadian treasury securities
Fair value on a recurring basis
Marketable securities		0
Fair Value, Measurements, Recurring \| Level 2
Fair value on a recurring basis
Cash and cash equivalents	0	0
Interest rate lock agreements	7,346,000
Total assets at fair value	7,346,000	70,405,000
Total liabilities at fair value		19,628,000
Fair Value, Measurements, Recurring \| Level 2 \| Interest rate lock agreement
Fair value on a recurring basis
Long term accrued liabilities		19,628,000
Fair Value, Measurements, Recurring \| Level 2 \| Canadian treasury securities
Fair value on a recurring basis
Marketable securities		70,405,000
Fair Value, Measurements, Recurring \| Level 3
Fair value on a recurring basis
Cash and cash equivalents	0	0
Interest rate lock agreements	0
Total assets at fair value	$ 0	0
Total liabilities at fair value		0
Fair Value, Measurements, Recurring \| Level 3 \| Interest rate lock agreement
Fair value on a recurring basis
Long term accrued liabilities		0
Fair Value, Measurements, Recurring \| Level 3 \| Canadian treasury securities
Fair value on a recurring basis
Marketable securities		$ 0

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

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=66048111&loc=d3e19207-110258

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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
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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
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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 20
-Section 55
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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Fair value portion of other assets.

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