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Revenue - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Disaggregation Of Revenue [Line Items]
Revenue	$ 13,384	$ 20,462
Accounts receivable	1,786	1,786	$ 813
Neurocrine Biosciences [Member]
Disaggregation Of Revenue [Line Items]
Accounts receivable	1,467	1,467
Deferred revenue	12,692	12,692
Neurocrine Biosciences [Member] \| Collaboration Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	13,384	20,462
Exclusive License to XEN901 and Exclusive License to DTCs [Member] \| Neurocrine Biosciences [Member] \| Collaboration Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	11,523	17,285
Development Services Under the Initial Development Program For DTCs [Member] \| Neurocrine Biosciences [Member] \| Collaboration Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	393	475
Research And Development Funding \| Neurocrine Biosciences [Member] \| Collaboration Revenue [Member]
Disaggregation Of Revenue [Line Items]
Revenue	$ 1,468	$ 2,702
License and Collaboration Agreement [Member] \| Neurocrine Biosciences [Member]
Disaggregation Of Revenue [Line Items]
Upfront payment received in cash			30,000
Upfront payment received in equity investment			20,000
Equity investment measured at fair value			16,667
Collaborate agreement premium related to equity investment			3,333
Transaction price allocated to performance obligations			$ 33,333
Percentage of option to co-fund development costs upon achievement of certain milestones			50.00%
License and Collaboration Agreement [Member] \| Exclusive License to XEN901 and Exclusive License to DTCs [Member] \| Neurocrine Biosciences [Member]
Disaggregation Of Revenue [Line Items]
Transaction price allocated to performance obligations			$ 28,807
License and Collaboration Agreement [Member] \| Development Services Under the Initial Development Program For DTCs [Member] \| Neurocrine Biosciences [Member]
Disaggregation Of Revenue [Line Items]
Transaction price allocated to performance obligations			$ 4,526