Summary of Significant Accounting Principles - Concentration of Credit Risk (Details)	9 Months Ended
	Sep. 30, 2021 agreement item	Sep. 30, 2020 item
Concentration of Credit Risk
Number of license agreements | agreement	7
Royalty
Concentration of Credit Risk
Number of license agreements | agreement	10
Revenue | Product concentration risk | Royalty
Concentration of Credit Risk
Number of license agreements | item	2	4
Concentration risk percentage	0.00%	0.00%
Revenue | Product concentration risk | Royalty | Licensees Two
Concentration of Credit Risk
Concentration risk percentage	98.00%
Revenue | Product concentration risk | Royalty | Licensees Four
Concentration of Credit Risk
Concentration risk percentage		88.00%
Revenue | Product concentration risk | Minimum | Royalty | Licensees Two
Concentration of Credit Risk
Concentration risk percentage	40.00%
Revenue | Product concentration risk | Minimum | Royalty | Licensees Four
Concentration of Credit Risk
Concentration risk percentage		19.00%
Revenue | Product concentration risk | Maximum | Royalty | Licensees Two
Concentration of Credit Risk
Concentration risk percentage	58.00%
Revenue | Product concentration risk | Maximum | Royalty | Licensees Four
Concentration of Credit Risk
Concentration risk percentage		29.00%
Accounts receivable | Credit concentration risk | Royalty
Concentration of Credit Risk
Number of license agreements | item	1	1
Concentration risk percentage	0.00%	0.00%
Accounts receivable | Credit concentration risk | Royalty | one receivable
Concentration of Credit Risk
Concentration risk percentage	100.00%	100.00%