Segment Information by Product Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenue from External Customer [Line Items]
Net product revenues	$ 302,190	$ 235,357
Vimizim
Revenue from External Customer [Line Items]
Net product revenues	105,821	72,578
Naglazyme
Revenue from External Customer [Line Items]
Net product revenues	80,558	65,403
Kuvan
Revenue from External Customer [Line Items]
Net product revenues	92,346	76,692
Aldurazyme
Revenue from External Customer [Line Items]
Net product revenues	19,355	16,445
Firdapse
Revenue from External Customer [Line Items]
Net product revenues	$ 4,110	$ 4,239