Net Loss per Share - Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share of Common Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	1,949,089	2,244,363	1,675,506
Restricted Stock Units for Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	1,898,025	2,279,081	1,044,651
Restricted Shares of Common Stock Subject to Repurchase [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	0	217,621	335,062
Restricted Stock Issued In Connection with Skyfence Acquisition [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	118,961	355,499	0