Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)					12 Months Ended
	Sep. 01, 2018	Jul. 28, 2017	Feb. 10, 2017	Dec. 22, 2015	Dec. 31, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Restricted cash					$ 1,800,000	$ 1,800,000
Outstanding claim					0
Impairment of long-lived assets					$ 0
Net proceeds form issuance of preferred stock		$ 83,500,000
Tax positions, description					The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency.
Collaboration revenue					$ 3,684,000
ASU 2014-09 | Minimum | Deferred Revenue
Summary Of Significant Accounting Policies [Line Items]
Effect of adoption of new accounting standard					(1,500,000)
ASU 2014-09 | Minimum | Collaboration Revenue
Summary Of Significant Accounting Policies [Line Items]
Effect of adoption of new accounting standard					1,500,000
ASU 2014-09 | Maximum | Deferred Revenue
Summary Of Significant Accounting Policies [Line Items]
Effect of adoption of new accounting standard					(2,000,000)
ASU 2014-09 | Maximum | Collaboration Revenue
Summary Of Significant Accounting Policies [Line Items]
Effect of adoption of new accounting standard					$ 2,000,000
Employee Stock Purchase Plan
Summary Of Significant Accounting Policies [Line Items]
Purchase of common stock through payroll deductions expressed in percentage of fair market value	85.00%				85.00%
Share based compensation, discount from market price					15.00%
Share based compensation arrangement by share based payment purchase period					180 days
Royalty
Summary Of Significant Accounting Policies [Line Items]
Collaboration revenue					$ 0
Series A Convertible Preferred Stock
Summary Of Significant Accounting Policies [Line Items]
Preferred stock shares issued			28,873,237	28,873,237		28,873,237
Preferred stock per share			$ 0.71
Net proceeds form issuance of preferred stock			$ 20,500,000	$ 20,500,000		$ 20,479,000