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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue from External Customer [Line Items]
Net product revenues	$ 387,763	$ 372,845	$ 788,508	$ 746,292
Aldurazyme
Revenue from External Customer [Line Items]
Net product revenues	5,826	24,003	51,093	90,059
Brineura
Revenue from External Customer [Line Items]
Net product revenues	14,795	10,890	26,975	17,807
Firdapse
Revenue from External Customer [Line Items]
Net product revenues	5,482	5,177	10,594	10,103
Kuvan
Revenue from External Customer [Line Items]
Net product revenues	113,323	109,045	220,247	208,160
Naglazyme
Revenue from External Customer [Line Items]
Net product revenues	98,127	91,086	185,054	166,082
Palynziq
Revenue from External Customer [Line Items]
Net product revenues	18,836	0	31,108	0
Vimizim
Revenue from External Customer [Line Items]
Net product revenues	122,686	127,585	248,487	244,674
Total net product revenues
Revenue from External Customer [Line Items]
Net product revenues	$ 379,075	$ 367,786	$ 773,558	$ 736,885