Retirement Plan (Details Textuals) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Defined Contribution Plan Employer Contribution Amount	$ 3.3	$ 2.5	$ 2.3

Amount of contributions made by an employer to a defined contribution plan.

No definition available.

Name:	xtxi_DefinedContributionPlanEmployerContributionAmount
Namespace Prefix:	xtxi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant