Stockholders' Equity - Schedule of change in retained earnings (Detail) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2018	Oct. 31, 2017
Equity [Abstract]
Beginning Balance	$ 2,022,988
Cumulative effect of the change in accounting principle, net of tax	(5,450)
Net income	13,953	$ 128,406
Dividends declared but not paid	(20,595)
Ending Balance	$ 2,010,896