Commitments and contingencies - Neurocrine Collaboration Agreement - (Details) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) item $ / shares shares	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($) shares	Dec. 31, 2019 USD ($)
Allocation of Transaction Price
Related party collaboration receivable	$ 12,686			$ 12,686		$ 18,496
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		$ 50,000
Price per share | $ / shares			$ 11.9625
Estimated cost reimbursement	340,400				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
Payment from June 2019 Modification					5,000
Discount related to equity investment					27,600
Allocation of Transaction Price
Allocation of variable consideration	340,442			340,442
Allocation of fixed consideration	92,382	$ 92,400		92,382	92,400
Revenue recognized	24,500	$ 12,500		38,900	14,400
Deferred revenue	50,100			50,100
Reimbursement costs expected to be received	12,700			12,700
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	83,983			83,983
Allocation of fixed consideration	80,373			80,373
Neurocrine Collaboration Agreement | Neurocrine | FA Program
Allocation of Transaction Price
Allocation of variable consideration	113,033			113,033
Allocation of fixed consideration	6,005			6,005
Neurocrine Collaboration Agreement | Neurocrine | Discovery program 1
Allocation of Transaction Price
Allocation of variable consideration	72,164			72,164
Allocation of fixed consideration	3,002			3,002
Neurocrine Collaboration Agreement | Neurocrine | Discovery program 2
Allocation of Transaction Price
Allocation of variable consideration	71,262			71,262
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