Collaboration and License Revenue - Schedule of Prepayments and Reimbursed Research and Development Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at beginning of year	$ 12,973
Balance at end of year		$ 12,973
Collaborative Agreement | Aventis Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at beginning of year	12,973	4,432
Additions for advance billings			$ 1,013
Payments received from Sanofi	5,521	31,659	10,697
Actual expenses incurred	$ (18,494)	(23,118)	(7,278)
Balance at end of year		$ 12,973	$ 4,432