Fair Value Measurements - Additional Information (Detail) (USD $)	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013
Fair Value Disclosures [Abstract]
Transfers between levels of fair value hierarchy	$ 0	$ 0

Amount of transfers of assets measured on a recurring basis between levels of the fair value hierarchy.

No definition available.

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