Condensed Consolidated Statements of Stockholders' Equity - USD ($)	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock
Beginning balance at Jul. 31, 2016	$ 470,401,000	$ 3,837,000	$ 524,797,000	$ 383,616,000	$ (441,849,000)
Common stock, beginning balance (in shares) at Jul. 31, 2016		38,367,997
Treasury stock, beginning balance (in shares) at Jul. 31, 2016					15,033,317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-classified stock award compensation	2,980,000		2,980,000
Proceeds from issuance of employee stock purchase plan shares	514,000	$ 5,000	509,000
Proceeds from issuance of employee stock purchase plan shares (in shares)		49,694
Issuance of restricted stock	0	$ 14,000	(14,000)
Issuance of restricted stock (in shares)		144,988
Net settlement of stock-based awards	(244,000)	$ 4,000	(248,000)
Net settlement of stock-based awards (in shares)		40,354
Cash dividends declared	(11,691,000)			(11,691,000)
Accrual of dividend equivalents, net of reversal	(228,000)			(228,000)
Net income tax shortfall from settlement of stock-based awards	(240,000)		(240,000)
Reversal of deferred tax assets associated with expired and unexercised stock-based awards	(350,000)		(350,000)
Net income	8,513,000			8,513,000
Ending balance at Apr. 30, 2017	469,655,000	$ 3,860,000	527,434,000	380,210,000	$ (441,849,000)
Common stock, ending balance (in shares) at Apr. 30, 2017		38,603,033
Treasury stock, ending balance (in shares) at Apr. 30, 2017					15,033,317
Beginning balance at Jul. 31, 2017	$ 480,150,000	$ 3,862,000	533,001,000	385,136,000	$ (441,849,000)
Common stock, beginning balance (in shares) at Jul. 31, 2017	38,619,467	38,619,467
Treasury stock, beginning balance (in shares) at Jul. 31, 2017	15,033,317				15,033,317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-classified stock award compensation	$ 2,931,000		2,931,000
Proceeds from exercises of stock options	130,000		130,000
Proceeds from exercises of stock options (in shares)		4,900
Proceeds from issuance of employee stock purchase plan shares	619,000	$ 4,000	615,000
Proceeds from issuance of employee stock purchase plan shares (in shares)		35,830
Forfeiture of restricted stock	0	$ (1,000)	1,000
Forfeiture of restricted stock (in shares)		(10,254)
Net settlement of stock-based awards	(1,055,000)	$ 3,000	(1,058,000)
Net settlement of stock-based awards (in shares)		25,358
Cash dividends declared	(7,055,000)			(7,055,000)
Accrual of dividend equivalents, net of reversal	(247,000)			(247,000)
Net income	22,311,000			22,311,000
Ending balance at Apr. 30, 2018	$ 497,784,000	$ 3,868,000	$ 535,620,000	$ 400,145,000	$ (441,849,000)
Common stock, ending balance (in shares) at Apr. 30, 2018	38,675,301	38,675,301
Treasury stock, ending balance (in shares) at Apr. 30, 2018	15,033,317				15,033,317