Liability Related to Sale of Future Royalties, net - Narrative (Details) $ / shares in Units, $ in Thousands	1 Months Ended		2 Months Ended	3 Months Ended	9 Months Ended
	Aug. 31, 2020 USD ($) unit_of_accounting	Jun. 30, 2018 USD ($) unit_of_accounting $ / shares shares	Feb. 29, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Liability For Sale of Future Royalties [Line Items]
Proceeds from sale of common stock			$ 282,833		$ 283,333	$ 303,221
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%	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
2020 RPI Funding 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	$ 147,876
Sales-based participation rights sold, value	$ 250,000
Percentage of global net sales of products containing zavegepant for basis of participation rights	3.00%
Percentage of global net sales of products containing rimegepant for basis of participation rights	0.40%
Proceeds from sale of sales-based participation rights	$ 150,000
Receivable related to sales-based participation rights	$ 100,000
Period from closing for repurchase if change of control consummated	180 days
Buy-Back option factor	2.0
Success-based milestone payments based on first zavegepant regulatory approval, relative to funded amount	1.9
Time period for success-based milestone payments	10 years
Transaction consideration allocated to obligation to perform contractual services	$ 2,124
Transaction costs	$ 400
Effective interest rate (percent)				6.00%	6.00%
Research And Development, Contra Expense				$ 110	$ 110
2020 RPI Funding Agreement | Minimum
Liability For Sale of Future Royalties [Line Items]
Success-based milestone payments based on regulatory approval, relative to funded amount	0.6
2020 RPI Funding Agreement | Maximum
Liability For Sale of Future Royalties [Line Items]
Success-based milestone payments based on regulatory approval, relative to funded amount	2.95