Accumulated Other Comprehensive Income (loss) (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
May 31, 2017	May 31, 2016	May 31, 2015
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Reclassification adjustments for gains included in net income, tax benefit	$ 401	$ 946	$ 2,307

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 11
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65896914&loc=d3e39076-109324

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration