Revenue, Credit Concentrations and Geographic Information - Disaggregates of Net Product Revenues by Product (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue from External Customer [Line Items]
Net product revenues	$ 429,485	$ 387,763	$ 931,554	$ 788,508
Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	386,740	373,249	820,117	722,465
Kuvan | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	122,611	113,323	244,611	220,247
Vimizim | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	116,695	122,686	253,898	248,487
Naglazyme | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	81,006	98,127	195,262	185,054
Palynziq | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	40,630	18,836	75,262	31,108
Brineura | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	25,798	14,795	49,768	26,975
Firdapse | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	0	5,482	1,316	10,594
Total net product revenues
Revenue from External Customer [Line Items]
Net product revenues	419,032	379,075	908,075	773,558
Total net product revenues | Marketed by Company
Revenue from External Customer [Line Items]
Net product revenues	386,740	373,249	820,117	722,465
Aldurazyme | Marketed by Genzyme
Revenue from External Customer [Line Items]
Net product revenues	$ 32,292	$ 5,826	$ 87,958	$ 51,093