Segment Information - Net Income Reconciliation (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total profit from reportable segments	$ 41,143	$ 35,020	$ 83,425	$ 74,539
Unallocated amounts:
Administrative costs	(6,347)	(5,058)	(13,218)	(11,369)
Investment and other income	1,056	596	1,272	107
Interest expense	(829)	(1,458)	(1,692)	(3,190)
Earnings before income taxes	$ 35,023	$ 29,100	$ 69,787	$ 60,087