Stock-Based Compensation - Performance Shares, RSUs, Restricted Stock and Share Unit Awards (Details)		3 Months Ended				9 Months Ended
	Jan. 31, 2018 USD ($) $ / shares shares	Apr. 30, 2018 USD ($) $ / shares shares	Jan. 31, 2018 $ / shares shares	Oct. 31, 2017 $ / shares shares	Apr. 30, 2017 USD ($)	Apr. 30, 2018 USD ($) $ / shares shares	Apr. 30, 2017 USD ($)	Jul. 31, 2017 USD ($)
Additional Disclosures
Accrual of dividend equivalents, net of reversal | $						$ 247,000	$ 228,000
Carrying value at period end | $		$ 336,288,000				$ 336,288,000		$ 351,913,000
Performance Shares, RSUs, Restricted Stock and Share Units
Awards (in Shares)
Outstanding, Beginning Balance (in shares)		970,713	975,550	830,197		830,197
Granted (in shares)		3,212		307,194
Settled (in shares)		(687)	(526)	(100,321)
Forfeited (in shares)		(4,886)	(4,311)	(61,520)
Outstanding, Ending Balance (in shares)	970,713	968,352	970,713	975,550		968,352
Vested, Ending Balance (in shares)		309,853				309,853
Vested and Expected to Vest, Ending Balance (in shares)		933,270				933,270
Weighted Average Grant Date Fair Value
Outstanding, Beginning Balance (in dollars per share) | $ / shares		$ 16.86	$ 16.86	$ 16.95		$ 16.95
Granted (in dollars per share) | $ / shares		28.37		18.25
Settled (in dollars per share) | $ / shares		11.04	11.40	20.67
Forfeited (in dollars per share) | $ / shares		15.36	15.26	18.88
Outstanding, Ending Balance (in dollars per share) | $ / shares	$ 16.86	16.91	$ 16.86	$ 16.86		16.91
Vested, Ending Balance (in dollars per share) | $ / shares		17.55				17.55
Vested and Expected to Vest, Ending Balance (in dollars per share) | $ / shares		$ 16.94				$ 16.94
Aggregate Intrinsic Value
Outstanding, Ending Balance | $		$ 29,622,000				$ 29,622,000
Vested, Ending Balance | $	$ 9,478,000
Vested and Expected to Vest, Ending Balance | $		28,549,000				28,549,000
Additional Disclosures
Total intrinsic value of stock-based awards settled | $		$ 17,000			$ 0	$ 1,964,000	$ 633,000
Performance Shares | Employees
Additional Disclosures
Common Stock conversion ratio		1				1
Performance Shares | Employees | Granted prior to fiscal 2014
Additional Disclosures
Vesting period (in years)						5 years 3 months 18 days
Performance Shares | Employees | Granted since fiscal 2014
Additional Disclosures
Performance period (in years)						3 years
RSUs and restricted stock | Non-Employee Director
Additional Disclosures
Vesting period (in years)						3 years
Common Stock conversion ratio		1				1
RSUs and restricted stock | Employees
Additional Disclosures
Vesting period (in years)						5 years
Common Stock conversion ratio		1				1
Share units
Additional Disclosures
Common Stock conversion ratio		1				1
Cumulative number of units settled as of the date (in shares)		14,777				14,777
Share units | Granted on or after July 31, 2017
Additional Disclosures
Conversion period of fully-vested share units into Common Stock from grant date (in years)						1 year
Stock Options
Additional Disclosures
Total intrinsic value of stock-based awards settled | $		$ 225,000				$ 225,000
Dividend Equivalents
Additional Disclosures
Accrual of dividend equivalents, net of reversal | $						247,000
Dividend equivalents paid | $						129,000
Carrying value at period end | $		$ 672,000				$ 672,000		$ 554,000
2000 Stock Incentive Plan | Performance Shares
Awards (in Shares)
Outstanding, Ending Balance (in shares)		278,860				278,860
2000 Stock Incentive Plan | RSUs and restricted stock
Awards (in Shares)
Outstanding, Ending Balance (in shares)		421,886				421,886
2000 Stock Incentive Plan | Share units
Awards (in Shares)
Outstanding, Ending Balance (in shares)		267,606				267,606