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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Concentration Risk [Line Items]
Concentration risk, percentage	56.00%	58.00%	52.00%	56.00%
Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	16.00%	16.00%	17.00%	17.00%
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	10.00%	10.00%	11.00%	10.00%
Customer D
Concentration Risk [Line Items]
Concentration risk, percentage	5.00%	7.00%	6.00%	11.00%
Customer E
Concentration Risk [Line Items]
Concentration risk, percentage	12.00%	0.00%	6.00%	0.00%
Customer F
Concentration Risk [Line Items]
Concentration risk, percentage	0.00%	13.00%	0.00%	6.00%