Consolidated Net Product Revenue Concentrations Based on Patient Location (Detail) - Net Product Revenue	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	93.00%	93.00%
Geographic Concentration Risk | United States
Concentration Risk [Line Items]
Concentration risk, percentage	37.00%	39.00%
Geographic Concentration Risk | Europe
Concentration Risk [Line Items]
Concentration risk, percentage	22.00%	25.00%
Geographic Concentration Risk | Latin America
Concentration Risk [Line Items]
Concentration risk, percentage	12.00%	8.00%
Geographic Concentration Risk | Rest of World
Concentration Risk [Line Items]
Concentration risk, percentage	22.00%	21.00%
Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	40.00%	44.00%
Customer Concentration Risk | Genzyme | Aldurazyme
Concentration Risk [Line Items]
Concentration risk, percentage	7.00%	7.00%
Credit Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	100.00%	100.00%