Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Collaboration and licensing revenues	$ 145,579	$ 109,871	$ 87,821
Related Parties, Aggregated
Related Party Transaction [Line Items]
Collaboration and licensing revenues	$ 130,670	$ 93,792	$ 77,354

Revenue from contractual agreements with collaborators whereby the collaborators obtain exclusive access to the entity's proprietary technologies for use in the research, development and commercialization of products and/or treatments in a contractually specified field of use as well as revenue earned during the period relating to consideration received from another party for the right to use, but not own, certain of the entity's intangible assets. Includes revenue recognized from upfront payments received upon consummation of the agreement, reimbursements for costs incurred by the entity for research and development efforts, and milestone payments received upon achievement of specified development, regulatory and commercial activities as defined in the collaboration and licensing agreements.

No definition available.

Name:	xon_CollaborationAndLicensingRevenue
Namespace Prefix:	xon_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration