Disaggregates of Total Net Product Revenues from External Customers by Product (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue from External Customer [Line Items]
Net product revenues	$ 372,845	$ 317,448	$ 746,292	$ 621,193
Aldurazyme
Revenue from External Customer [Line Items]
Net product revenues	24,003	19,985	90,059	39,340
Brineura
Revenue from External Customer [Line Items]
Net product revenues	10,890	254	17,807	254
Firdapse
Revenue from External Customer [Line Items]
Net product revenues	5,177	4,855	10,103	8,965
Kuvan
Revenue from External Customer [Line Items]
Net product revenues	109,045	101,944	208,160	194,290
Naglazyme
Revenue from External Customer [Line Items]
Net product revenues	91,086	85,751	166,082	166,309
Vimizim
Revenue from External Customer [Line Items]
Net product revenues	127,585	103,137	244,674	208,958
Net Product Revenues
Revenue from External Customer [Line Items]
Net product revenues	$ 367,786	$ 315,926	$ 736,885	$ 618,116