Basic and Diluted Net Loss Per Share - Schedule of Common Equivalent Shares were Excluded From Diluted Net Loss Per Share Calculation because their Inclusion would have been Anti-Dilutive (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per share	5,973,473	6,679,809	1,968,215
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per share	1,746,073	2,440,290	1,884,425
Shares To Be Issued Under ESSP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per share	22,683	44,320	83,790
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per share	793,518	784,000
Convertible Senior Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from diluted net loss per share	3,411,199	3,411,199