Stockholders' Equity - Additional Information (Detail)					1 Months Ended	12 Months Ended			17 Months Ended	20 Months Ended
	Sep. 07, 2017 shares	Aug. 07, 2017 USD ($) $ / shares shares	Jul. 27, 2017 USD ($)	Feb. 04, 2016 USD ($)	Sep. 07, 2017 $ / shares	Dec. 31, 2017 USD ($) transaction shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) shares	Nov. 01, 2017 USD ($)	Aug. 03, 2017 USD ($)
Class of Stock [Line Items]
Repurchase of common stock				$ 500,000,000		$ 402,393,000	$ 187,979,000	$ 8,119,000
Repurchase of common stock						$ 402,393,000	$ 187,678,000	$ 0
Shares acquired (in shares) | shares	263,012	1,491,647				2,854,959				4,114,104
Initial price paid (in usd per share) | $ / shares		$ 142.46
Final price paid (in usd per share) | $ / shares					$ 142.48
Number of transactions | transaction						2
Repurchase agreements
Class of Stock [Line Items]
Repurchase of common stock						$ 402,400,000			$ 590,100,000	$ 590,100,000
Repurchase of common stock		$ 250,000,000
Common Stock
Class of Stock [Line Items]
Stock repurchase program, period in force				18 months
Increase in authorized amount of repurchases			$ 250,000,000								$ 350,000,000
Extension of original period			18 months
Aggregate authorized repurchase amount											$ 1,100,000,000
Remaining authorized repurchase amount			$ 510,000,000
Common Stock | Repurchase agreements
Class of Stock [Line Items]
Aggregate authorized repurchase amount												$ 250,000,000