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FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2012 | Dec. 31, 2011
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Significant Other Observable Inputs (level 2) | Recurring basis |  |
Summarizes the valuation of interest rate swaps and impaired assets |  |
Interest rate swaps asset (liability) | $ (15,531) | $ (19,446)
Significant Unobservable Inputs (Level 3) | Nonrecurring basis |  |
Summarizes the valuation of interest rate swaps and impaired assets |  |
Impaired long-lived assets | $ 1,800 |

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- Definition Interest rate swaps asset liability fair value disclosure. + References No definition available. + Details
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Namespace Prefix: | exh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Long-lived asset impairment fair value disclosure. + References No definition available. + Details
Name: | exh_LongLivedAssetImpairmentFairValueDisclosure
Namespace Prefix: | exh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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