Earnings Per Common Share - Computation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018
Numerator for basic and diluted earnings per share:
Net income	$ (5,583)	$ 15,787	$ (2,263)	$ 5,767	$ 8,825	$ 8,175	$ 18,800	$ 19,242	$ 13,708	$ 55,042	$ 91,041
Less income allocated to participating securities									(1)	(51)	(320)
Net income available to common shareholders									$ 13,707	$ 54,991	$ 90,721
Denominator for basic and diluted earnings per share, as adjusted for participating securities:
Denominator for basic earnings per share - weighted average number of shares outstanding attributable to common stock (in shares)									42,238,282	41,700,926	41,567,722
Dilutive effect of stock options using the treasury stock method and the average market price for the year (in shares)									45,643	56,190	67,356
Dilutive effect of convertible debt outstanding (in shares)									25,291	0	0
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock (in shares)									42,309,216	41,757,116	41,635,078
Earnings per share attributable to common stock:
Basic earnings per share (in dollars per share)	$ (0.13)	$ 0.37	$ (0.05)	$ 0.14	$ 0.21	$ 0.20	$ 0.45	$ 0.46	$ 0.32	$ 1.32	$ 2.18
Diluted earnings per share (in dollars per share)	$ (0.13)	$ 0.37	$ (0.05)	$ 0.14	$ 0.21	$ 0.20	$ 0.45	$ 0.46	$ 0.32	$ 1.32	$ 2.18
Stock options excluded from weighted average dilutive common shares outstanding because their inclusion would have been antidilutive (in shares)									0	0	0