Stockholders' Equity - Share Repurchases (Details) - USD ($)	3 Months Ended			12 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Mar. 31, 2017	Dec. 31, 2011
Stockholders' Equity Note [Abstract]
Share repurchase program, authorized amount for repurchase					$ 1,000,000,000.0	$ 500,000,000.0
Share repurchase program, common stock repurchased (in shares)	0	0	24,500	0
Share repurchase program, common stock repurchased			$ 6,100,000
Share repurchase program, average purchase price (in dollars per share)			$ 248.70
Share repurchase program, remaining authorized amount for repurchase	$ 557,400,000