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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue from External Customer [Line Items]
Net product revenues	$ 476,784	$ 461,097	$ 1,408,338	$ 1,249,605
Vimizim | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	147,891	163,466	401,789	411,953
Kuvan | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	123,993	120,524	368,604	340,771
Naglazyme | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	76,323	94,408	271,585	279,462
Palynziq | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	46,092	24,142	121,354	55,250
Brineura | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	25,455	19,840	75,223	46,815
Firdapse | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	0	5,668	1,316	16,262
Total net product revenues
Revenue from External Customer [Line Items]
Net product revenues	460,741	450,900	1,368,816	1,224,458
Total net product revenues | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	419,754	428,048	1,239,871	1,150,513
Aldurazyme | Marketed by Genzyme
Revenue from External Customer [Line Items]
Net product revenues	$ 40,987	$ 22,852	$ 128,945	$ 73,945