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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Concentration Risk [Line Items]
Concentration risk, percentage	43.00%	47.00%	47.00%	51.00%
Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	16.00%	18.00%	17.00%	18.00%
Customer B
Concentration Risk [Line Items]
Concentration risk, percentage	13.00%	12.00%	12.00%	12.00%
Customer C
Concentration Risk [Line Items]
Concentration risk, percentage	12.00%	10.00%	11.00%	9.00%
Customer D
Concentration Risk [Line Items]
Concentration risk, percentage	2.00%	7.00%	7.00%	12.00%