Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Options Outstanding
Number Outstanding (in shares)	122,500	122,500
Weighted Average Exercise Price (in dollars per share)	$ 29.36	$ 29.36
Weighted Average Remaining Contractual Life	15 months 7 days
Aggregate Intrinsic Value	$ 5,493
Options Exercisable
Number Exercisable (in shares)	104,167
Weighted Average Exercise Price (in dollars per share)	$ 26.28
Weighted Average Remaining Contractual Life	12 months 7 days
Aggregate Intrinsic Value	$ 4,992
Stock-based awards, additional disclosure
Deduction in income tax due to exercise of options and vesting of restricted stock (in dollars)	5,592	$ 3,059
Reduction in income tax expense over the equity awards' vesting period	3,351	1,880
Share-based compensation, excess tax benefit, amount	2,241	1,179
Stock options
Options Outstanding
Aggregate Intrinsic Value	$ 5,493	$ 4,605	$ 3,133
Stock options, additional disclosure
Options vested during period (in shares)	23,333	35,834	27,500
Aggregate fair value of all options vested (in dollars)	$ 349	$ 344	$ 248
Weighted average fair value of all options granted (in dollars per share)		$ 26.49	$ 11.54
Outstanding options (in shares)	122,500	122,500	107,500
Exercise of stock options (in shares)	89,607	67,038
Total average price per share	$ 77.12	$ 55.68