Segment Information by Product Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenue from External Customer [Line Items]
Net product revenues	$ 315,926	$ 298,576	$ 618,116	$ 533,933
Vimizim
Revenue from External Customer [Line Items]
Net product revenues	103,137	106,829	208,958	179,407
Brineura
Revenue from External Customer [Line Items]
Net product revenues	254	0	254	0
Naglazyme
Revenue from External Customer [Line Items]
Net product revenues	85,751	78,444	166,309	143,847
Kuvan
Revenue from External Customer [Line Items]
Net product revenues	101,944	90,215	194,290	166,907
Aldurazyme
Revenue from External Customer [Line Items]
Net product revenues	19,985	18,623	39,340	35,068
Firdapse
Revenue from External Customer [Line Items]
Net product revenues	$ 4,855	$ 4,465	$ 8,965	$ 8,704