Disaggregates of Total Net Product Revenues Based on Patient Location (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Net product revenues	$ 391,706	$ 334,148	$ 1,137,998	$ 955,341
United States
Disaggregation Of Revenue [Line Items]
Net product revenues	174,722	151,012	528,082	425,107
Europe
Disaggregation Of Revenue [Line Items]
Net product revenues	111,069	121,268	323,940	292,845
Latin America
Disaggregation Of Revenue [Line Items]
Net product revenues	55,322	9,546	151,955	121,581
Rest of World
Disaggregation Of Revenue [Line Items]
Net product revenues	50,593	52,322	134,021	115,808
Aldurazyme
Disaggregation Of Revenue [Line Items]
Net product revenues	27,593	22,341	117,652	61,681
Net Product Revenues
Disaggregation Of Revenue [Line Items]
Net product revenues	386,320	298,752	1,123,205	916,868
Marketed by Company | Brineura, Firdapse, Kuvan, Naglazyme, and Vimizim
Disaggregation Of Revenue [Line Items]
Net product revenues	358,727	276,411	1,005,553	855,187
Marketed by Company | Brineura, Firdapse, Kuvan, Naglazyme, and Vimizim | United States
Disaggregation Of Revenue [Line Items]
Net product revenues	146,742	127,302	409,294	361,264
Marketed by Company | Brineura, Firdapse, Kuvan, Naglazyme, and Vimizim | Europe
Disaggregation Of Revenue [Line Items]
Net product revenues	107,851	88,646	315,270	260,223
Marketed by Company | Brineura, Firdapse, Kuvan, Naglazyme, and Vimizim | Latin America
Disaggregation Of Revenue [Line Items]
Net product revenues	55,322	9,549	151,955	121,581
Marketed by Company | Brineura, Firdapse, Kuvan, Naglazyme, and Vimizim | Rest of World
Disaggregation Of Revenue [Line Items]
Net product revenues	48,812	50,914	129,034	112,119
Marketed by Genzyme | Aldurazyme
Disaggregation Of Revenue [Line Items]
Net product revenues	$ 27,593	$ 22,341	$ 117,652	$ 61,681