Stockholders' Equity - Schedule of Share Repurchase Authorized by Board of Directors (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($)
April, 2014 [Member]
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Authorization	$ 200,000,000
Expiration	Dec. 31, 2015
February, 2015 [Member]
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Authorization	$ 150,000,000
Expiration	Dec. 31, 2016
January, 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Authorization	$ 200,000,000
Expiration	Dec. 31, 2017
April, 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Authorization	$ 113,182,000
Expiration	Dec. 31, 2017
November, 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Authorization	$ 236,000,000
Expiration	Dec. 31, 2018
October, 2017 [Member]
Equity, Class of Treasury Stock [Line Items]
Share Repurchase Authorization	$ 200,000,000
Expiration	Dec. 31, 2019