Revenue - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
	Sep. 09, 2019	Sep. 30, 2019	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Transaction price		$ 3,500	$ 3,500
Asset Purchase Agreement [Member] | Flexion [Member] | XEN402 [Member]
Disaggregation Of Revenue [Line Items]
Proceeds from upfront fee	$ 3,000
Asset Purchase Agreement [Member] | Flexion [Member] | XEN402 [Member] | ASC 606 [Member]
Disaggregation Of Revenue [Line Items]
Proceeds from initiation of first GLP toxicology study	500
Asset Purchase Agreement [Member] | Maximum [Member] | Flexion [Member] | Eligible to Receive CMC Development and Regulatory Milestone Payments [Member] | XEN402 [Member]
Disaggregation Of Revenue [Line Items]
Transaction price	9,000
Asset Purchase Agreement [Member] | Maximum [Member] | Flexion [Member] | Future Clinical Development And Global Regulatory Approval Milestone Payments [Member] | XEN402 [Member]
Disaggregation Of Revenue [Line Items]
Transaction price	40,750
Asset Purchase Agreement [Member] | Maximum [Member] | Flexion [Member] | Commercial Milestone Payments [Member] | XEN402 [Member]
Disaggregation Of Revenue [Line Items]
Transaction price	$ 75,000