Stockholders' Equity - Narrative (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Nov. 01, 2018	May 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity
Shares of common stock, authorized (in shares)			600,000,000	600,000,000
Shares of common stock, issued and sold (in shares)			180,175,355	174,275,864
Repurchases and retirement of common stock (in shares)		540,806
Repurchases and retirement of common stock		$ 55,000		$ 55,000
Repurchases and retirement of common stock (in USD per share)		$ 101.70
Settlement of 2018 Notes conversion feature (in shares)	1,300,000
Preferred stock, shares authorized (in shares)			10,000,000	10,000,000
Preferred stock, shares outstanding (in shares)			0	0
Common Stock
Stockholders' Equity
Common stock issued under employee stock plans (in shares)			5,899,519	7,385,897	6,645,009
Repurchases and retirement of common stock (in shares)				540,806
Settlement of 2018 Notes conversion feature (in shares)			1,313,617