Stock-Based Compensation (Details 2) (USD $)	1 Months Ended	9 Months Ended		3 Months Ended
	Apr. 30, 2015	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2015	Apr. 30, 2014	Jul. 31, 2014
Stock-Based Compensation
Total unrecognized stock-based compensation expense, before income taxes, related to total nonvested stock options and stock awards (in dollars)	$ 7,696,000	$ 7,696,000		$ 7,696,000
Remaining weighted average period over which unrecognized stock-based compensation expense is expected to be recognized	18 months
Stock-based awards, additional disclosure
Deduction in income tax due to exercise of options and vesting of restricted stock (in dollars)		4,532,000	5,124,000
Increase in additional paid-in capital due to excess tax benefit on stock-based compensation expense (in dollars)		2,662,000	3,815,000
Restricted shares
Number of Shares
Nonvested stock awards at the beginning of the period (in shares)		525,842
Granted (in shares)		120,599
Cancelled (in shares)		(12,210)
Vested (in shares)		(292,177)
Nonvested stock awards at the end of the period (in shares)	342,054	342,054		342,054
Weighted Average Fair Value
Nonvested stock awards at the beginning of the period (in dollars per share)		$ 22.25
Granted (in dollars per share)		$ 37.84
Cancelled (in dollars per share)		$ 25.93
Vested (in dollars per share)		$ 17.82
Nonvested stock awards at the end of the period (in dollars per share)	$ 31.39	$ 31.39		$ 31.39
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)		$ 2,803,000	$ 3,747,000	$ 383,000	$ 1,328,000
Number of Shares
Outstanding at the beginning of the period (in shares)		222,492
Granted (in shares)		25,000	30,000
Exercised (in shares)		(89,367)
Outstanding at the end of the period (in shares)	158,125	158,125		158,125
Exercisable at the end of the period (in shares)	95,625	95,625		95,625		157,492
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)		$ 12.78
Granted (in dollars per share)		$ 36.70
Exercised (in dollars per share)		$ 7.14
Outstanding at the end of the period (in dollars per share)	$ 19.75	$ 19.75		$ 19.75
Exercisable at the end of the period (in dollars per share)	$ 13.30	$ 13.30		$ 13.30		$ 8.21