Royalty Purchase Agreements - Summary of Acquisition of Royalty Rights (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at beginning of period	$ 34,575
Balance at end of period	48,075
Viracta
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Acquisition of royalty rights	$ 13,500