Common Stock - Share Repurchase of Common Stock (Detail) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Aggregate purchase price	$ 422,166	$ 455,351	$ 431,367
Number of shares repurchased (in Shares)	167	280	290