Acquisitions	9 Months Ended
Sep. 30, 2018
Business Combinations [Abstract]
Acquisitions	Acquisitions In September 2018, the Company expanded its pipeline by acquiring the rights and related intellectual property of ten gene therapy programs through its acquisition of Celenex. Celenex is a private, clinical stage gene therapy company whose lead programs are ten gene therapy programs including CLN6 and CLN3, which are in clinical stage, and several programs in pre-clinical stage. Pursuant to the terms of the agreement, the Company acquired Celenex for cash consideration of $100 million. The Company has also agreed to pay up to an additional $15 million in connection with the achievement of certain development milestones, $262 million in connection with the achievement of certain regulatory approval milestones across multiple programs and up to $75 million in tiered sales milestone payments. Celenex has an exclusive license agreement with Nationwide Children’s Hospital (“NCH”). Under this license agreement, NCH is eligible to receive development and sales based milestones of up to $7.8 million for each product. The Company evaluated the Celenex transaction based on the guidance in Business Combinations (Topic 805) and concluded that the transaction did not meet the definition of a business and was an asset acquisition. Given the fact that the license has no alternative future use, the $100.0 million upfront payment was expensed to research and development expense in the Consolidated Statements of Operations for the three and nine months ended September 30, 2018 in accordance with ASC Topic 730, Research and Development.

Acquisitions

In September 2018, the Company expanded its pipeline by acquiring the rights and related intellectual property of ten gene therapy programs through its acquisition of Celenex. Celenex is a private, clinical stage gene therapy company whose lead programs are ten gene therapy programs including CLN6 and CLN3, which are in clinical stage, and several programs in pre-clinical stage. Pursuant to the terms of the agreement, the Company acquired Celenex for cash consideration of $100 million. The Company has also agreed to pay up to an additional $15 million in connection with the achievement of certain development milestones, $262 million in connection with the achievement of certain regulatory approval milestones across multiple programs and up to $75 million in tiered sales milestone payments. Celenex has an exclusive license agreement with Nationwide Children’s Hospital (“NCH”). Under this license agreement, NCH is eligible to receive development and sales based milestones of up to $7.8 million for each product.

The Company evaluated the Celenex transaction based on the guidance in Business Combinations (Topic 805) and concluded that the transaction did not meet the definition of a business and was an asset acquisition. Given the fact that the license has no alternative future use, the $100.0 million upfront payment was expensed to research and development expense in the Consolidated Statements of Operations for the three and nine months ended September 30, 2018 in accordance with ASC Topic 730, Research and Development.