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Fair Value Measurements (Details 2)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014
Long-term receivable from the sale of Canadian Operations
Fair value measurement of assets and liabilities
Discount rate (as a percent)	13.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByAssetClassAxis = exh_LongTermReceivableFromSaleOfDiscontinuedOperationsMember
Settlement period	5 years 6 months
Impaired long-lived assets
Fair value measurement of assets and liabilities
Weighted average disposal period of impaired assets		4 years
Impaired long-lived assets | Weighted average
Fair value measurement of assets and liabilities
Discount rate (as a percent)		9.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByAssetClassAxis = exh_ImpairedLongLivedAssetsMember / us-gaap_RangeAxis = us-gaap_WeightedAverageMember

X

- Definition

Represents the settlement period used as an input to measure fair value.

+ References

No definition available.

+ Details

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X

- Definition

Weighted average disposal period used to find the present value of an amount to be paid or received in the future as an input to measure fair value.

+ References

No definition available.

+ Details

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- Details

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X

- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Details

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