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Commitments and Contingencies (Details Textual) (USD $)
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3 Months Ended | 9 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|
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Feb. 28, 2014
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May 31, 2013
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Feb. 28, 2014
Line of Credit [Member]
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Feb. 28, 2014
Revolving Credit Facility [Member]
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Nov. 30, 2013
Revolving Credit Facility [Member]
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Aug. 31, 2013
Revolving Credit Facility [Member]
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Feb. 28, 2014
Revolving Credit Facility [Member]
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Feb. 28, 2014
Standby Letters of Credit [Member]
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May 31, 2013
Standby Letters of Credit [Member]
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| Line of Credit Facility [Line Items] | |||||||||
| Maximum amount outstanding during period | $ 0 | $ 175,000,000 | $ 25,000,000 | ||||||
| Interest rate on amount borrowed | 3.25% | 3.25% | |||||||
| Maximum borrowing capacity | 500,000,000 | 500,000,000 | |||||||
| Expiration date | Jun. 21, 2018 | ||||||||
| Amount outstanding | 0 | 0 | 0 | ||||||
| Amount available | 43,000,000 | 36,800,000 | |||||||
| Expiration date range of letters of credit | July 2014 and April 2015 | ||||||||
| Irrevocable stand by letters of credit amount outstanding | 0 | ||||||||
| Commitments and Contingencies (Textual) | |||||||||
| Commitments to purchase capital assets | $ 7,700,000 | $ 9,900,000 | |||||||