Commitments and contingencies - Neurocrine Collaboration Agreement - (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) item $ / shares shares	Jun. 30, 2019 USD ($) shares	Sep. 30, 2019 USD ($)
Neurocrine | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option after paying rate-shifting fee		60.00%
Neurocrine Collaboration Agreement | Parkinson's Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option		50.00%
Percentage of profit or loss under co-co option after paying rate-shifting fee		45.00%
Neurocrine Collaboration Agreement | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option after paying rate-shifting fee		40.00%
Neurocrine Collaboration Agreement | Neurocrine
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of collaboration programs | item		4
Number of discovery programs | item		2
Programs added later | item		2
Number of targets | item		8
Upfront payment		$ 115,000	$ 115,000
Purchase of common stock, shares | shares		4,179,728	4,179,728
Purchase of common stock		$ 50,000	$ 5,000
Price per share | $ / shares		$ 11.9625
Estimated cost reimbursement			431,100
Termination period		10 years
Period of advance notice for termination prior to first commercial sale		180 days
Period of advance notice for termination after first commercial sale		1 year
Discount related to equity investment			27,600
Equity investment			50,000
Allocation of Transaction Price
Allocation of variable consideration	$ 431,064			$ 431,064
Allocation of fixed consideration	92,382		92,400	92,382
Revenue recognized	16,800			31,100
Deferred revenue	83,300			83,300
Reimbursement costs expected to be received	14,000			14,000
Costs to obtain collaboration agreement	800			800
Consideration received			$ 5,000
Neurocrine Collaboration Agreement | Neurocrine | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of reduction in royalty payments		50.00%
Neurocrine Collaboration Agreement | Neurocrine | Parkinson's Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option		50.00%
Rate-shifting fee		$ 35,000
Percentage of profit or loss under co-co option after paying rate-shifting fee		55.00%
Allocation of Transaction Price
Allocation of variable consideration	170,209			170,209
Allocation of fixed consideration	80,373			80,373
Neurocrine Collaboration Agreement | Neurocrine | FA Program
Allocation of Transaction Price
Allocation of variable consideration	114,023			114,023
Allocation of fixed consideration	6,005			6,005
Neurocrine Collaboration Agreement | Neurocrine | Discovery program 1
Allocation of Transaction Price
Allocation of variable consideration	73,416			73,416
Allocation of fixed consideration	3,002			3,002
Neurocrine Collaboration Agreement | Neurocrine | Discovery program 2
Allocation of Transaction Price
Allocation of variable consideration	73,416			73,416
Allocation of fixed consideration	$ 3,002			$ 3,002
Neurocrine Collaboration Agreement | Neurocrine | Development and regulatory milestones | Parkinson's Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		$ 170,000
Neurocrine Collaboration Agreement | Neurocrine | Development and regulatory milestones | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		195,000
Neurocrine Collaboration Agreement | Neurocrine | Development and regulatory milestones | Discovery program 1
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		130,000
Neurocrine Collaboration Agreement | Neurocrine | Commercial Milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per Milestone, maximum milestone payments to be received from collaborative partner		275,000
Aggregate maximum milestone payments to be received from collaborative partner		$ 1,100,000