Collaboration and License Revenue - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended			24 Months Ended
	Jul. 31, 2019	Jan. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Repurchase of royalty rights			$ 80,000,000
Deferred revenue					$ 33,558,000
Contract assets			0
Contract liabilities			0
Collaborative Agreement | Sanofi (Aventis Inc.)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable continuation payment received		$ 45,000,000.0
Revenue recognized on pro-rata basis to research and development effort						$ 45,000,000.0
Continuation payment, amount received		$ 45,000,000.0
Fixed fee						45,000,000.0
Transaction price for extended term						45,000,000.0
Collaboration and license revenue			0	$ 33,600,000	11,400,000
Deferred revenue			0
Reduction in research and development expenses due to RPP reimbursements			$ 18,500,000	$ 23,100,000	$ 7,300,000
Collaborative Agreement | Sanofi (Aventis Inc.) | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Funding from approved in-kind research and clinical activities						$ 45,000,000.0
Termination Agreement | Sanofi (Aventis Inc.) | Royalty Rights
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment received for research and development	$ 80,000,000.0
Repurchase of royalty rights	50,000,000.0
Transferred to escrow	30,000,000.0
Research and development asset reacquired	$ 4,300,000