Earnings Per Share (Details) (USD $)	3 Months Ended		6 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2015	Jan. 31, 2014
Earnings Per Share [Abstract]
Net income for basic calculation	$ 7,585,000	$ 5,983,000	$ 12,810,000	$ 11,288,000
Interest expense (net of tax) on 3.0% convertible senior notes	0	1,117,000	0	2,234,000
Numerator for diluted calculation	7,585,000	7,100,000	12,810,000	13,522,000
Denominator for basic calculation (in shares)	16,241,000	15,970,000	16,229,000	16,212,000
Dilutive effect on shares of stock-based awards (in shares)	264,000	287,000	281,000	141,000
Dilutive effect on shares of conversion of 3.0% convertible senior notes (in shares)	0	6,230,000	0	6,199,000
Denominator for diluted calculation (in shares)	16,505,000	22,487,000	16,510,000	22,552,000
Debt Instrument, Face Amount		$ 200,000,000		$ 200,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.00%		3.00%
Reduction in weighted average number of shares as a result of the repurchase of common shares		439,000		289,000
Treasury Stock, Shares, Acquired	0		0	935,992
Weighted average performance shares outstanding during the period that are excluded from EPS calculation	120,000	92,000	119,000	70,000
Stock-Based Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive equity-classified stock-based awards not included in calculation of diluted earnings per share (in shares)	447,000	573,000	287,000	2,308,000