Stockholders' Equity - Schedule of Stock Repurchases (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stockholders Equity [Line Items]
Total cost			$ 14,220
2016 Stock Repurchase Program
Stockholders Equity [Line Items]
Shares of common stock repurchased and retired	0	1,887	0	2,767
Average price paid per share	$ 0.00	$ 34.74	$ 42.17	$ 37.03
Total cost	$ 0	$ 65,556	$ 14,213	$ 102,457