Investments - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017	Jul. 31, 2017
Investment [Line Items]
Sale (purchase) of Trading Securities	$ 2,200	$ 13,800	$ 8,000
Gains (losses) on Trading Securities	2,509	1,876	2,603
Trading securities		0		$ 11,898
Cash
Investment [Line Items]
Gains (losses) on Trading Securities	400	4,600	900
Non Cash
Investment [Line Items]
Gains (losses) on Trading Securities	$ 2,200	$ (2,700)	$ 1,700

Amount of cash inflow (outflow) from sales and purchases of trading securities.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3098-108585

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

Name:	us-gaap_ProceedsFromPaymentsForTradingSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration