Schedule of Stock Award Activity (Detail) - $ / shares	12 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Jul. 31, 2013
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, beginning of year, Shares	13,620	17,530	10,041
Granted, Shares			9,498
Vested, Shares	(3,907)	(3,910)	(2,009)
Nonvested, end of year, Shares	9,713	13,620	17,530
Nonvested, beginning of year, Weighted Average Grant Date Fair Value	$ 31.08	$ 31.03	$ 29.46
Granted, Weighted Average Grant Date Fair Value			32.36
Vested, Weighted Average Grant Date Fair Value	30.87	30.87	29.46
Nonvested, end of year, Weighted Average Grant Date Fair Value	$ 31.16	$ 31.08	$ 31.03
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, beginning of year, Shares	212,073	139,275
Granted, Shares	162,967	151,168	143,069
Vested, Shares	(90,608)	(63,852)
Forfeited, Shares	(4,079)	(14,518)	(3,794)
Nonvested, end of year, Shares	280,353	212,073	139,275
Nonvested, beginning of year, Weighted Average Grant Date Fair Value	$ 49.21	$ 38.06
Granted, Weighted Average Grant Date Fair Value	50.95	54.26	$ 38.01
Vested, Weighted Average Grant Date Fair Value	48.14	38.68
Forfeited, Weighted Average Grant Date Fair Value	50.54	47.26	36.32
Nonvested, end of year, Weighted Average Grant Date Fair Value	$ 50.55	$ 49.21	$ 38.06