Multiple Performance Conditions for Vesting Of Base RSUs (Detail) - Restricted Stock With Performance and Market Based Vesting Conditions - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units, outstanding	860,000	860,000
Restricted stock units, earned	799,800
Product Goals | Approval of Vimizim In US or EU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Base RSUs to Vest Upon Achievement of Goal	35.00%
Base Number of RSUs Granted Before TSR Multiplier	301,000
Performance Goal Attained	Yes
Number of RSUs Earned After TSR Multiplier	373,240
Product Goals | Approval of pegvaliase (Peg Pal) or Any Other Non Vimizim Product In US Or EU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Base RSUs to Vest Upon Achievement of Goal	25.00%
Base Number of RSUs Granted Before TSR Multiplier	215,000
Performance Goal Attained	No
Financial Goal
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Base RSUs to Vest Upon Achievement of Goal	40.00%
Base Number of RSUs Granted Before TSR Multiplier	344,000
Performance Goal Attained	Yes
Number of RSUs Earned After TSR Multiplier	426,560