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)
Beginning balance (in shares) at Jul. 31, 2016		38,367,997
Beginning balance (in shares) at Jul. 31, 2016					15,033,317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-classified stock award compensation	8,467,000		8,467,000
Proceeds from issuance of employee stock purchase plan shares	694,000	$ 7,000	687,000
Proceeds from issuance of employee stock purchase plan shares (in shares)		64,367
Issuance of restricted stock, net	0	$ 14,000	(14,000)
Issuance of restricted stock, net (in shares)		144,988
Net settlement of stock-based awards	(262,000)	$ 4,000	(266,000)
Net settlement of stock-based awards (in shares)		42,115
Cash dividends declared	(14,034,000)			(14,034,000)
Accrual of dividend equivalents, net of reversal	(273,000)			(273,000)
Net income tax shortfall from settlement of stock-based awards	(248,000)		(248,000)
Reversal of deferred tax assets associated with expired and unexercised stock-based awards	(422,000)		(422,000)
Net income	15,827,000			15,827,000
Ending balance at Jul. 31, 2017	480,150,000	$ 3,862,000	533,001,000	385,136,000	$ (441,849,000)
Ending balance (in shares) at Jul. 31, 2017		38,619,467
Ending balance (in shares) at Jul. 31, 2017					15,033,317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-classified stock award compensation	8,605,000		8,605,000
Proceeds from issuance of employee stock purchase plan shares	855,000	$ 5,000	850,000
Proceeds from issuance of employee stock purchase plan shares (in shares)		44,996
Proceeds from exercises of stock options	326,000	$ 1,000	325,000
Proceeds from exercises of stock options (in shares)		13,100
Forfeiture of restricted stock	0	$ (1,000)	1,000
Forfeiture of restricted stock (in shares)		(10,254)
Net settlement of stock-based awards	$ (4,310,000)	$ 19,000	(4,329,000)
Net settlement of stock-based awards (in shares)	8,706	193,262
Cash dividends declared	$ (9,411,000)			(9,411,000)
Accrual of dividend equivalents, net of reversal	(300,000)			(300,000)
Net income	29,769,000			29,769,000
Ending balance at Jul. 31, 2018	$ 505,684,000	$ 3,886,000	538,453,000	405,194,000	$ (441,849,000)
Ending balance (in shares) at Jul. 31, 2018	38,860,571	38,860,571
Ending balance (in shares) at Jul. 31, 2018	15,033,317				15,033,317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-classified stock award compensation	$ 11,427,000		11,427,000
Proceeds from issuance of employee stock purchase plan shares	926,000	$ 4,000	922,000
Proceeds from issuance of employee stock purchase plan shares (in shares)		43,316
Proceeds from exercises of stock options	216,000	$ 1,000	215,000
Proceeds from exercises of stock options (in shares)		8,100
Issuance of restricted stock, net	0	$ 1,000	(1,000)
Issuance of restricted stock, net (in shares)		10,386
Net settlement of stock-based awards	$ (3,916,000)	$ 15,000	(3,931,000)
Net settlement of stock-based awards (in shares)	9,345	145,119
Common stock issued for acquisition of Solacom Technologies, Inc.	$ 5,606,000	$ 21,000	5,585,000
Common stock issued for acquisition of Solacom Technologies, Inc. (in shares)		208,669
Cash dividends declared	(9,575,000)			(9,575,000)
Accrual of dividend equivalents, net of reversal	(327,000)			(327,000)
Net income	25,041,000			25,041,000
Ending balance at Jul. 31, 2019	$ 535,082,000	$ 3,928,000	$ 552,670,000	$ 420,333,000	$ (441,849,000)
Ending balance (in shares) at Jul. 31, 2019	39,276,161	39,276,161
Ending balance (in shares) at Jul. 31, 2019	15,033,317				15,033,317