Revenue, Credit Concentrations and Geographic Information - Total Net Product Revenue Concentrations Attributed to Largest Customers (Detail) - Customer Concentration Risk - Net Product Revenue	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Concentration Risk [Line Items]
Concentration risk, percentage	42.00%	51.00%	44.00%	46.00%
Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	16.00%	16.00%	15.00%	17.00%
Customer B
Concentration Risk [Line Items]
Concentration risk, percentage	14.00%	13.00%	14.00%	12.00%
Customer C
Concentration Risk [Line Items]
Concentration risk, percentage	11.00%	10.00%	12.00%	11.00%
Customer D
Concentration Risk [Line Items]
Concentration risk, percentage	1.00%	12.00%	3.00%	6.00%