Schedule of Restricted Stock Award Activity (Detail) - $ / shares	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, beginning of year, Shares	5,806	9,713	13,620
Vested, Shares	(3,907)	(3,907)	(3,907)
Nonvested, end of year, Shares	1,899	5,806	9,713
Nonvested, beginning of year, Weighted Average Grant Date Fair Value	$ 31.36	$ 31.16	$ 31.08
Vested, Weighted Average Grant Date Fair Value	30.87	30.87	30.87
Nonvested, end of year, Weighted Average Grant Date Fair Value	$ 32.36	$ 31.36	$ 31.16
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, beginning of year, Shares	325,136	280,353	212,073
Granted, Shares	166,567	181,872	162,967
Vested, Shares	(157,315)	(133,758)	(90,608)
Forfeited, Shares	(1,812)	(3,331)	(4,079)
Nonvested, end of year, Shares	332,576	325,136	280,353
Nonvested, beginning of year, Weighted Average Grant Date Fair Value	$ 53.95	$ 50.55	$ 49.21
Granted, Weighted Average Grant Date Fair Value	84.85	55.37	50.95
Vested, Weighted Average Grant Date Fair Value	53.87	48.73	48.14
Forfeited, Weighted Average Grant Date Fair Value	64.03	54.18	50.54
Nonvested, end of year, Weighted Average Grant Date Fair Value	$ 69.41	$ 53.95	$ 50.55