Revenue - Product Revenue Allowance and Reserves (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disclosure Of Product Revenue Reserves And Allowances [Line Items]
Beginning balance at January 1, 2020	$ 2,241	$ 0
Provision related to sales in the current year	1,048	265
Adjustments related to prior period sales	(217)
Deductions applied and payments made	(1,096)	(8)
Ending balance at March 31, 2020	1,976	257
Chargebacks, Discounts and Fees [Member]
Disclosure Of Product Revenue Reserves And Allowances [Line Items]
Beginning balance at January 1, 2020	1,618	0
Provision related to sales in the current year	612	189
Adjustments related to prior period sales	(267)
Deductions applied and payments made	(639)	(8)
Ending balance at March 31, 2020	1,324	181
Government and Other Rebates [Member]
Disclosure Of Product Revenue Reserves And Allowances [Line Items]
Beginning balance at January 1, 2020	271	0
Provision related to sales in the current year	175	76
Deductions applied and payments made	(262)
Ending balance at March 31, 2020	184	76
Returns [Member]
Disclosure Of Product Revenue Reserves And Allowances [Line Items]
Beginning balance at January 1, 2020	352	0
Provision related to sales in the current year	261
Adjustments related to prior period sales	50
Deductions applied and payments made	(195)
Ending balance at March 31, 2020	$ 468	$ 0