Liability Related to Sale of Future Royalties - Narrative (Details) - USD ($)	1 Months Ended	9 Months Ended
	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Liability For Sale of Future Royalties [Line Items]
Proceeds from sale of common stock	$ 49,889,000	$ 55,000,000	$ 179,996,000
RPI Agreement
Liability For Sale of Future Royalties [Line Items]
Proceeds from royalty agreement	149,623,000
Transaction consideration allocated to liability	106,047,000
Transaction consideration allocated to equity	43,953,000
Transaction costs	377,000
RPI Funding Agreement
Liability For Sale of Future Royalties [Line Items]
Proceeds from royalty agreement	$ 100,000,000
Percentage of revenue participation rights available for repurchase (percent)	100.00%
Price of revenue participation rights available for repurchase	$ 155,000,000
Effective interest rate (percent)	20.00%
RPI Funding Agreement | Revenue Participation Right, tranche one
Liability For Sale of Future Royalties [Line Items]
Participation rate for revenue participation right (percent)	2.10%
RPI Funding Agreement | Revenue Participation Right, tranche one | Maximum
Liability For Sale of Future Royalties [Line Items]
Annual global net sales threshold for revenue participation right	$ 1,500,000,000
RPI Funding Agreement | Revenue Participation Right, tranche two
Liability For Sale of Future Royalties [Line Items]
Participation rate for revenue participation right (percent)	1.50%
RPI Funding Agreement | Revenue Participation Right, tranche two | Minimum
Liability For Sale of Future Royalties [Line Items]
Annual global net sales threshold for revenue participation right	$ 1,500,000,000
RPI Purchase Agreement
Liability For Sale of Future Royalties [Line Items]
Common stock sold (shares)	1,111,111
Common stock sold, price per share (in dollars per share)	$ 45.00
Proceeds from sale of common stock	$ 50,000,000