Consolidated Net Product Revenue Concentrations Based on Patient Location (Detail) - Net Product Revenue	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Geographic Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	94.00%	94.00%	94.00%	93.00%
Geographic Concentration Risk | United States
Concentration Risk [Line Items]
Concentration risk, percentage	38.00%	36.00%	38.00%	37.00%
Geographic Concentration Risk | Europe
Concentration Risk [Line Items]
Concentration risk, percentage	21.00%	22.00%	21.00%	23.00%
Geographic Concentration Risk | Latin America
Concentration Risk [Line Items]
Concentration risk, percentage	18.00%	17.00%	15.00%	13.00%
Geographic Concentration Risk | Rest of World
Concentration Risk [Line Items]
Concentration risk, percentage	17.00%	19.00%	20.00%	20.00%
Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	51.00%	50.00%	47.00%	48.00%
Customer Concentration Risk | Genzyme | Aldurazyme
Concentration Risk [Line Items]
Concentration risk, percentage	6.00%	6.00%	6.00%	7.00%
Credit Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	100.00%	100.00%	100.00%	100.00%