Disaggregates of Total Net Product Revenues from External Customers by Product (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Net product revenues	$ 1,704,048	$ 1,491,212	$ 1,313,646
Aldurazyme
Revenue from External Customer [Line Items]
Net product revenues	97,809	135,097	89,959
Brineura
Revenue from External Customer [Line Items]
Net product revenues	71,997	39,889	8,595
Firdapse
Revenue from External Customer [Line Items]
Net product revenues	22,348	21,787	18,890
Kuvan
Revenue from External Customer [Line Items]
Net product revenues	463,353	433,582	407,542
Naglazyme
Revenue from External Customer [Line Items]
Net product revenues	374,334	345,851	332,208
Palynziq
Revenue from External Customer [Line Items]
Net product revenues	86,857	12,173	0
Vimizim
Revenue from External Customer [Line Items]
Net product revenues	544,345	481,977	413,251
Product
Revenue from External Customer [Line Items]
Net product revenues	$ 1,661,043	$ 1,470,356	$ 1,270,445