Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Shares that were Excluded from Computation of Diluted Net Income (Loss) per Share of Common Stock (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock-based awards [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential common shares excluded from computation of net loss per share	9,630,761	9,738,595
Convertible senior notes [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential common shares excluded from computation of net loss per share	1,527,584	2,370,788
Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential common shares excluded from computation of net loss per share	301,504	595,104