Net Product Revenue - Summary of Balances and Activity in Each of Product Revenue Allowance and Reserve Categories (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at December 31, 2018	$ 1,820	$ 348
Provision related to current period sales	2,149	582
Adjustment related to prior period sales	3	(30)
Credits or payments made during the period	(1,052)	(104)
Balance at March 31, 2019	2,920	796
Chargebacks, Discounts and Fees [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at December 31, 2018	270	50
Provision related to current period sales	470	155
Adjustment related to prior period sales	(66)	0
Credits or payments made during the period	(498)	(104)
Balance at March 31, 2019	176	101
Government and Other Rebates [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at December 31, 2018	1,353	293
Provision related to current period sales	1,621	375
Adjustment related to prior period sales	69	(30)
Credits or payments made during the period	(554)	0
Balance at March 31, 2019	2,489	638
Returns [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at December 31, 2018	197	5
Provision related to current period sales	58	52
Adjustment related to prior period sales	0	0
Credits or payments made during the period	0	0
Balance at March 31, 2019	$ 255	$ 57