Stockholders' Equity - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Number of Units outstanding, beginning of year (in shares)	1,330	1,139	1,226
Number of Units, Granted (in shares)	1,731	718	516
Number of Units, Released (in shares)	(519)	(414)	(488)
Number of Units, Forfeited (in shares)	(194)	(113)	(115)
Number of Units outstanding, end of year (in shares)	2,348	1,330	1,139
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value, Units outstanding, beginning of year (in dollars per share)	$ 20.40	$ 19.30	$ 13.23
Weighted Average Grant Date Fair Value, Granted (in dollars per share)	24.59	19.75	26.18
Weighted Average Grant Date Fair Value, Released (in dollars per share)	18.85	15.91	11.82
Weighted Average Grant Date Fair Value, Forfeited (in dollars per share)	24.61	21.65	16.72
Weighted Average Grant Date Fair Value, Units outstanding, end of year (in dollars per share)	$ 23.47	$ 20.40	$ 19.30
Aggregate intrinsic value at year end	$ 62,222