License Agreements - BMS Agreement (Details) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended			9 Months Ended
	May 31, 2017 shares	Jul. 31, 2016 USD ($) item $ / shares	Feb. 29, 2016 $ / shares shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jul. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
License agreements
Net proceeds							$ 40,000
Common shares value issued							176,128
Fair value of common share | $ / shares		$ 7.70	$ 7.00			$ 7.70
Issuance of common shares | shares			429,000			1,090,500
Change in fair value of contingent equity liability							13,082	$ 13,125
Research and development				$ 34,996	$ 27,045		66,755	$ 35,137
BMS Agreement | Product related collaborative arrangements
License agreements
Common shares value issued		$ 12,500
Fair value of common share | $ / shares		$ 9.2911				$ 9.2911
Issuance of common shares | shares	1,345,374
Change in fair value of contingent equity liability				0			8,809
Research and development				$ 5,000			$ 5,000
BMS Agreement | Product related collaborative arrangements | Maximum
License agreements
Milestone payment to be paid		$ 127,500
Milestone payment to be paid for any product other than rimegepant		74,500
Commercial milestone payment to be paid		$ 150,000
Right to purchase shares fully diluted (as a percent)		8				8
BMS Agreement | Product related collaborative arrangements | Minimum
License agreements
Number of licensed products | item		1
Net proceeds		$ 30,000
Minimum investment in equity		$ 22,000				$ 22,000