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Summary of Securities in Unrealized Loss Position and Included in Accumulated Other Comprehensive (Loss), Aggregated by Length of Time Investments (Detail) - USD ($) $ in Thousands | Aug. 31, 2017 | May 31, 2017
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Investments Debt And Equity Securities [Abstract] |  |
Total investments with unrealized losses, fair value | $ 44,094 | $ 59,987
Unrealized losses with a loss position for less than 12 months, fair value | 9,808 | 40,854
Unrealized losses with a loss position for more than 12 months, fair value | 34,286 | 19,133
Total investments with unrealized losses, gross unrealized losses | (3,381) | (3,505)
Unrealized losses with a loss position for less than 12 months, gross unrealized losses | (208) | (2,983)
Unrealized losses with a loss position for more than 12 months, gross unrealized losses | $ (3,173) | $ (522)

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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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