Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions	1 Months Ended		3 Months Ended
	Jan. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2018 Segment PerformanceObligation
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of reportable and operating segment | Segment			1
Sanofi (Aventis Inc.) | Collaborative Agreement
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Continuation payment, amount received | $	$ 45.0	$ 45.0
Number of performance obligations | PerformanceObligation			3