Stock Repurchase Program - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended			4 Months Ended	6 Months Ended
	May 31, 2019	Feb. 28, 2019	Apr. 30, 2019	Apr. 30, 2018	Jan. 31, 2018	May 31, 2019	Apr. 30, 2019	Apr. 30, 2018	Apr. 05, 2018
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount			$ 500,000,000.0				$ 500,000,000.0		$ 500,000,000.0
Remaining amount available for further repurchases			$ 195,800,000				$ 195,800,000
Purchases of treasury stock (in shares)			780,000	916,000			1,126,000	2,902,000
accelerated Share repurchase program February 2019 ASR
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount		$ 100,000,000.0
Prepayment to repurchase stock		100,000,000.0
Initial share delivery		$ 80,000,000.0
Accelerated Share Repurchase Program September 2017
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, prepayment during prior period, derivative settlement					$ 20,000,000.0
Open Market Share Repurchase
Equity, Class of Treasury Stock [Line Items]
Purchases of treasury stock (in shares)				400,000
Shares repurchased average price per share (in USD per share)				$ 82.61
Shares repurchased during period				$ 35,000,000.0
Subsequent Event | accelerated Share repurchase program February 2019 ASR
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, prepayment during prior period, derivative settlement	$ 20,000,000.0
Purchases of treasury stock (in shares)	97,601					900,000
Shares repurchased average price per share (in USD per share)						$ 114.01