Consolidated Statements of Stockholders' Equity - USD ($)	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock
Beginning balance at Jul. 31, 2015	$ 401,409,000	$ 3,117,000	$ 427,083,000	$ 413,058,000	$ (441,849,000)
Common stock shares issued, beginning of period (in shares) at Jul. 31, 2015		31,165,401
Treasury stock shares outstanding, beginning of period (in shares) at Jul. 31, 2015					15,033,317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued from equity offering, net of issuance costs	94,070,000	$ 715,000	93,355,000
Common stock issued from equity offering, net of issuance costs (in shares)		7,145,000
Equity-classified stock award compensation	4,076,000		4,076,000
Proceeds from issuance of employee stock purchase plan shares	676,000	$ 4,000	672,000
Proceeds from issuance of employee stock purchase plan shares (in shares)		45,319
Net settlement of stock-based awards	(105,000)	$ 1,000	(106,000)
Net settlement of stock-based awards (in shares)		12,277
Cash dividends declared	(21,549,000)			(21,549,000)
Accrual of dividend equivalents, net of reversal	(155,000)			(155,000)
Net income tax shortfall from settlement of stock-based awards	(27,000)		(27,000)
Reversal of deferred tax assets associated with expired and unexercised stock-based awards	(256,000)		(256,000)
Net income (loss)	(7,738,000)			(7,738,000)
Ending balance at Jul. 31, 2016	470,401,000	$ 3,837,000	524,797,000	383,616,000	$ (441,849,000)
Common stock shares issued, end of period (in shares) at Jul. 31, 2016		38,367,997
Treasury stock shares outstanding, end of period (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 (loss)	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)
Common stock shares issued, end of period (in shares) at Jul. 31, 2017	38,619,467	38,619,467
Treasury stock shares outstanding, end of period (in shares) at Jul. 31, 2017	15,033,317				15,033,317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity-classified stock award compensation	$ 8,605,000		8,605,000
Proceeds from exercises of stock options	326,000	$ 1,000	325,000
Proceeds from exercises of stock options (in shares)		13,100
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
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 (loss)	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)
Common stock shares issued, end of period (in shares) at Jul. 31, 2018	38,860,571	38,860,571
Treasury stock shares outstanding, end of period (in shares) at Jul. 31, 2018	15,033,317				15,033,317