Schedule of Restricted Stock Award Activity (Detail) - $ / shares	12 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, beginning of year, Shares	9,713	13,620	17,530
Vested, Shares	(3,907)	(3,907)	(3,910)
Nonvested, end of year, Shares	5,806	9,713	13,620
Nonvested, beginning of year, Weighted Average Grant Date Fair Value	$ 31.16	$ 31.08	$ 31.03
Vested, Weighted Average Grant Date Fair Value	30.87	30.87	30.87
Nonvested, end of year, Weighted Average Grant Date Fair Value	$ 31.36	$ 31.16	$ 31.08
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, beginning of year, Shares	280,353	212,073	139,275
Granted, Shares	181,872	162,967	151,168
Vested, Shares	(133,758)	(90,608)	(63,852)
Forfeited, Shares	(3,331)	(4,079)	(14,518)
Nonvested, end of year, Shares	325,136	280,353	212,073
Nonvested, beginning of year, Weighted Average Grant Date Fair Value	$ 50.55	$ 49.21	$ 38.06
Granted, Weighted Average Grant Date Fair Value	55.37	50.95	54.26
Vested, Weighted Average Grant Date Fair Value	48.73	48.14	38.68
Forfeited, Weighted Average Grant Date Fair Value	54.18	50.54	47.26
Nonvested, end of year, Weighted Average Grant Date Fair Value	$ 53.95	$ 50.55	$ 49.21