Stock-Based Compensation (Details 2) - USD ($)	12 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Jul. 31, 2013
Stock-Based Compensation
Total unrecognized stock-based compensation expense, before income taxes, related to total nonvested stock options and stock awards (in dollars)	$ 7,491,000
Remaining weighted average period over which unrecognized stock-based compensation expense is expected to be recognized	17 months
Weighted-Average Black-Scholes Option Valuation Assumptions
Dividend yield (as a percent)	0.20%
Stock-based awards, additional disclosure
Deduction in income tax due to exercise of options and vesting of restricted stock (in dollars)	$ 5,317,000	$ 5,905,000
Increase in additional paid-in capital due to excess tax benefit on stock-based compensation expense (in dollars)	$ 3,168,000	$ 4,391,000
Restricted shares
Number of Shares
Nonvested stock awards at the beginning of the period (in shares)	525,842	605,767	708,008
Granted (in shares)	144,278	258,760	210,484
Cancelled (in shares)	(12,804)	(10,066)	(14,244)
Vested (in shares)	(313,797)	(328,619)	(298,481)
Nonvested stock awards at the end of the period (in shares)	343,519	525,842	605,767
Weighted Average Fair Value
Nonvested stock awards at the beginning of the period (in dollars per share)	$ 22.25	$ 11.96	$ 9.15
Granted (in dollars per share)	39.77	31.95	17.55
Cancelled (in dollars per share)	26.20	15.70	11.31
Vested (in dollars per share)	18.62	11.13	9.26
Nonvested stock awards at the end of the period (in dollars per share)	$ 32.77	$ 22.25	$ 11.96
Stock options
Weighted-Average Black-Scholes Option Valuation Assumptions
Dividend yield (as a percent)	0.25%	0.28%
Expected volatility (as a percent)	33.90%	42.70%
Risk-free interest rate (as a percent)	1.55%	1.44%
Expected lives	5 years	5 years
Stock options, additional disclosure
Weighted average fair value of all options granted (in dollars per share)	$ 11.54	$ 12.08
Aggregate intrinsic value of all options exercised (in dollars)	$ 5,178,000	$ 5,702,000	$ 6,616,000
Aggregate fair value of all options vested (in dollars)	$ 248,000	$ 127,000	$ 677,000
Number of Shares
Outstanding at the beginning of the period (in shares)	222,492	403,831	823,235
Granted (in shares)	25,000	30,000	52,500
Canceled (in shares)			(9,000)
Exercised (in shares)	(139,992)	(211,339)	(462,904)
Outstanding at the end of the period (in shares)	107,500	222,492	403,831
Exercisable at the end of the period (in shares)	45,000	157,492	351,331
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 12.78	$ 8.25	$ 6.57
Granted (in dollars per share)	36.70	31.81	17.04
Canceled (in dollars per share)			8.40
Exercised (in dollars per share)	7.11	6.82	6.26
Outstanding at the end of the period (in dollars per share)	25.73	12.78	8.25
Exercisable at the end of the period (in dollars per share)	$ 20.32	$ 8.21	$ 6.94
Aggregate intrinsic value of outstanding options (in dollars)	$ 3,133,000	$ 4,616,000