Segment Information - Net Income Reconciliation (Detail) - USD ($) $ in Thousands	3 Months Ended
Oct. 31, 2017	Oct. 31, 2016
Segment Reconciliation [Abstract]
Total profit from reportable segments	$ 42,282	$ 39,518
Unallocated amounts:
Administrative costs	(6,871)	(6,310)
Investment and other income	216	(489)
Interest expense	(863)	(1,732)
Earnings before income taxes	$ 34,764	$ 30,987

Amount of the cost of borrowed funds accounted for as interest expense.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.9)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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Balance Type:	debit
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