Consolidated Statements Of Changes In Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Income
Beginning balance at Jul. 31, 2014	$ 512,580	$ 619	$ 125,679	$ 378,477	$ 7,805
Beginning balance (in shares) at Jul. 31, 2014		12,372,992
Shares issued for:
Stock options exercised	7,274	$ 7	7,267
Stock options exercised (in shares)		135,444
Stock grants and vesting of restricted stock units, net of shares retained for taxes	(2,830)	$ 5	(2,835)
Stock grants and vesting of restricted stock units, net of shares retained for taxes (in shares)		92,743
Stock purchase plan	617	$ (1)	618
Stock purchase plan (in shares)		9,449
Share-based compensation expense	10,836		10,836
Tax benefit from share-based compensation	764		764
Repurchase of common stock	(13,872)	$ (9)	(1,791)	(12,072)
Repurchase of common stock (in shares)		(176,611)
Dividends declared ($0.40 per share)	(5,129)			(5,129)
Net income (loss) for the year	33,481			33,481
Other comprehensive income (loss), net of tax	(12,311)				(12,311)
Ending balance at Jul. 31, 2015	531,410	$ 621	140,538	394,757	(4,506)
Ending balance (in shares) at Jul. 31, 2015		12,434,017
Shares issued for:
Stock options exercised	4,174	$ 3	4,171
Stock options exercised (in shares)		61,384
Stock grants and vesting of restricted stock units, net of shares retained for taxes	(2,724)	$ 3	(2,727)
Stock grants and vesting of restricted stock units, net of shares retained for taxes (in shares)		65,087
Stock purchase plan	550	$ 1	549
Stock purchase plan (in shares)		8,176
Share-based compensation expense	8,739		8,739
Tax deficiency from share-based compensation	(324)		(324)
Repurchase of common stock	(13,698)	$ (9)	(1,941)	(11,748)
Repurchase of common stock (in shares)		(171,899)
Dividends declared ($0.40 per share)	(5,123)			(5,123)
Net income (loss) for the year	12,127			12,127
Other comprehensive income (loss), net of tax	(3,954)				(3,954)
Ending balance at Jul. 31, 2016	$ 531,177	$ 619	149,005	390,013	(8,460)
Ending balance (in shares) at Jul. 31, 2016	12,396,765	12,396,765
Shares issued for:
Stock options exercised	$ 2,794	$ 2	2,792
Stock options exercised (in shares)		56,808
Stock grants and vesting of restricted stock units, net of shares retained for taxes	(2,202)	$ 3	(2,205)
Stock grants and vesting of restricted stock units, net of shares retained for taxes (in shares)		66,839
Stock purchase plan	567	$ 1	566
Stock purchase plan (in shares)		8,698
Share-based compensation expense	9,432		9,432
Tax deficiency from share-based compensation	(946)		(946)
Repurchase of common stock	(4,410)	$ (3)	(737)	(3,670)
Repurchase of common stock (in shares)		(61,286)
Dividends declared ($0.40 per share)	(5,002)			(5,002)
Net income (loss) for the year	(74,237)			(74,237)
Other comprehensive income (loss), net of tax	3,321				3,321
Ending balance at Jul. 31, 2017	$ 460,494	$ 622	$ 157,907	$ 307,104	$ (5,139)
Ending balance (in shares) at Jul. 31, 2017	12,467,824	12,467,824