Reconciliation of Earnings (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Net income (loss)	$ 65,089	$ (2,906)	$ 59,852	$ (11,449)
Less: Preferred dividends on redeemable preferred stock	(259)		(259)
Net income (loss) attributable to common stockholders	64,830	(2,906)	59,593	(11,449)
Effect of dilutive securities:
Net income (loss) attributable to common stockholders after assumed conversions	$ 66,837	$ (2,906)	$ 63,311	$ (11,449)
Weighted average common shares outstanding	58,341	55,083	56,776	55,031
Weighted average common equivalent shares arising from dilutive stock options, restricted stock, convertible notes and convertible preferred stock	20,742		16,107
Weighted average number of common and potential common shares	79,083	55,083	72,883	55,031
Basic net earning (loss) per share attributable to common stockholders:	$ 1.11	$ (0.05)	$ 1.05	$ (0.21)
Diluted net earning (loss) per share attributable to common stockholders:	$ 0.85	$ (0.05)	$ 0.87	$ (0.21)
5.25% Convertible Senior Notes
Effect of dilutive securities:
Dilutive securities	$ 1,748		$ 3,459
Contingent Convertible Preferred Stock
Effect of dilutive securities:
Dilutive securities	$ 259		$ 259