Liability Related to Sale of Future Royalties, net - Narrative (Details) $ / shares in Units, $ in Thousands	1 Months Ended	2 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($) unit_of_accounting $ / shares shares	Feb. 29, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Liability For Sale of Future Royalties [Line Items]
Proceeds from sale of common stock		$ 282,833	$ 283,333	$ 282,000
RPI Agreement
Liability For Sale of Future Royalties [Line Items]
Units of accounting related to consideration received | unit_of_accounting	2
Transaction consideration allocated to liability	$ 106,047
Transaction consideration allocated to equity	43,953
Transaction costs	377
2018 RPI Funding Agreement
Liability For Sale of Future Royalties [Line Items]
Proceeds from royalty agreement	$ 100,000
Effective interest rate (percent)			27.00%
RPI Purchase Agreement
Liability For Sale of Future Royalties [Line Items]
Common stock issued (shares) | shares	1,111,111
Common stock sold, price per share (in dollars per share) | $ / shares	$ 45.00
Proceeds from sale of common stock	$ 50,000