Product Revenue Reserves and Allowances - Product Revenue Allowance and Reserves (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Disclosure of Product Revenue Reserves and Allowances [Line Items]
Beginning balance at January 1, 2019	$ 0
Provision related to sales in the current year	1,140
Credits and payments made	(89)
Ending balance at June 30, 2019	1,051
Chargebacks, Discounts and Fees [Member]
Disclosure of Product Revenue Reserves and Allowances [Line Items]
Beginning balance at January 1, 2019	0
Provision related to sales in the current year	877
Credits and payments made	(89)
Ending balance at June 30, 2019	788
Government and Other Rebates [Member]
Disclosure of Product Revenue Reserves and Allowances [Line Items]
Beginning balance at January 1, 2019	0
Provision related to sales in the current year	76
Ending balance at June 30, 2019	76
Returns [Member]
Disclosure of Product Revenue Reserves and Allowances [Line Items]
Beginning balance at January 1, 2019	0
Provision related to sales in the current year	187
Ending balance at June 30, 2019	$ 187