Revenue - Narrative (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
Disaggregation of Revenue [Line Items]
Revenue	$ 13,060	$ 32,099	$ 44,382	$ 77,516
Current deferred revenue	7,609		7,609		$ 7,323
Deferred revenue, long-term	12,706		12,706		14,732
Contract asset	13,461	$ 8,439	13,461	8,439	11,253	$ 0
Customer deposits reclassified to refund liabilities			0	$ 6,083
License | Customer in Asia Pacific in Patent Cross-License Agreement
Disaggregation of Revenue [Line Items]
Revenue	700		8,000
Current deferred revenue	3,500		3,500		3,400
Deferred revenue, long-term	12,100		12,100		13,700
Contract asset	$ 13,500		$ 13,500		$ 11,300