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Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Apr. 30, 2015
Canadian Operations |  |  |
Fair value measurement of assets and liabilities |  |  |
Settlement amount for outstanding note receivable |  |  | $ 5.1 exh_LongTermReceivableFromSaleOfDiscontinuedOperationsSettlementAmount / us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis = exh_CanadaOperationsMember
Impaired long-lived assets |  |  |
Fair value measurement of assets and liabilities |  |  |
Weighted average disposal period of impaired assets | 4 years | 4 years |
Discount rate (as a percent) | 10.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByAssetClassAxis = exh_ImpairedLongLivedAssetsMember | 9.00%us-gaap_FairValueInputsDiscountRate / us-gaap_FairValueByAssetClassAxis = exh_ImpairedLongLivedAssetsMember |

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- 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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Namespace Prefix: | exh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the settlement amount of long-term receivable from sale of discontinued operations. + References No definition available. + Details
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Namespace Prefix: | exh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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- 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 + Details
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- Details
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Namespace Prefix: |
Data Type: | na
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Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |