Collaborations	9 Months Ended
Sep. 30, 2018
Collaborative Arrangement [Abstract]
Collaboratives	Collaborations In October 2018, the Company further expanded its gene therapy portfolio through a collaboration agreement with Penn to pursue research and development of novel gene therapies for four additional indications, including Pompe disease, Fabry disease, CDD and one additional undisclosed rare metabolic disorder. This relationship will combine the Company's protein engineering and glycobiology expertise with Penn’s AAV gene transfer technologies to develop AAV gene therapies designed for optimal cellular uptake, targeting, dosing, safety and manufacturability. In connection with the collaboration agreement, the Company made an upfront payment of $7 million in cash to Penn in October 2018 and agreed to certain milestone payments following the achievement of certain developmental and commercial milestone events by a licensed product in each indication up to an aggregate of $86.5 million per indication.

Collaborations

9 Months Ended

Sep. 30, 2018

Collaborative Arrangement [Abstract]

Collaborations

In October 2018, the Company further expanded its gene therapy portfolio through a collaboration agreement with Penn to pursue research and development of novel gene therapies for four additional indications, including Pompe disease, Fabry disease, CDD and one additional undisclosed rare metabolic disorder. This relationship will combine the Company's protein engineering and glycobiology expertise with Penn’s AAV gene transfer technologies to develop AAV gene therapies designed for optimal cellular uptake, targeting, dosing, safety and manufacturability. In connection with the collaboration agreement, the Company made an upfront payment of $7 million in cash to Penn in October 2018 and agreed to certain milestone payments following the achievement of certain developmental and commercial milestone events by a licensed product in each indication up to an aggregate of $86.5 million per indication.