Segment Information - Net Income Reconciliation (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total profit from reportable segments	$ 35,020	$ 29,352	$ 74,539	$ 64,165
Unallocated amounts:
Administrative costs	(5,058)	(5,763)	(11,369)	(10,474)
Investment and other income	596	(992)	107	(1,751)
Interest expense	(1,458)	(2,130)	(3,190)	(4,281)
Earnings before income taxes	$ 29,100	$ 20,467	$ 60,087	$ 47,659