Commitments and Contingencies - Purchase Commitments (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Outstanding contractual purchase commitments	$ 15,802

Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services under long-term purchase commitments.

No definition available.

Name:	xon_LongtermPurchaseCommitmentRemainingMinimumAmountCommitted
Namespace Prefix:	xon_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant