Collaboration and Licensing Revenue - Summarized Collaboration and Licensing Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 21,561	$ 23,583	$ 79,652	$ 83,845
Collaboration and licensing agreements
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	22	5,223	389	20,259
Upfront and milestone payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenues	22	5,213	380	19,654
ZIOPHARM Oncology, Inc. | Collaboration and licensing agreements
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	0	0	0	100
Oragenics, Inc. | Collaboration and licensing agreements
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	0	2,823	0	3,053
Castle Creek Biosciences, Inc. | Collaboration and licensing agreements
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	18	2,394	371	16,967
Other | Collaboration and licensing agreements
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 4	$ 6	$ 18	$ 139