Collaboration Agreements - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Collaboration agreements
Contract assets	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Contract liabilities
Deferred revenue beginning balance			3,987	4,815
Deferred revenue, Additions			0	0
Deferred revenue, Deductions			32	817
Deferred revenue ending balance	3,955	3,998	3,955	3,998
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	11	11	32	817
Performance obligations satisfied in previous periods	$ 0	$ 0	$ 0	$ 0