Revenue, Credit Concentrations and Geographic Information - Disaggregates of Net Product Revenues by Product (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue from External Customer [Line Items]
Net product revenues	$ 461,097	$ 391,706	$ 1,249,605	$ 1,137,998
Aldurazyme
Revenue from External Customer [Line Items]
Net product revenues	22,852	27,593	73,945	117,652
Brineura
Revenue from External Customer [Line Items]
Net product revenues	19,840	9,936	46,815	27,743
Firdapse
Revenue from External Customer [Line Items]
Net product revenues	5,668	4,977	16,262	15,080
Kuvan
Revenue from External Customer [Line Items]
Net product revenues	120,524	113,254	340,771	321,414
Naglazyme
Revenue from External Customer [Line Items]
Net product revenues	94,408	103,089	279,462	269,171
Palynziq
Revenue from External Customer [Line Items]
Net product revenues	24,142	4,129	55,250	4,129
Vimizim
Revenue from External Customer [Line Items]
Net product revenues	163,466	123,342	411,953	368,016
Total net product revenues
Revenue from External Customer [Line Items]
Net product revenues	$ 450,900	$ 386,320	$ 1,224,458	$ 1,123,205