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Investments in Non-Consolidated Affiliates (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014
Investments in Non-Consolidated Affiliates |  |
Late installment payment received from the sale of the joint venture | $ 5.0 exh_EquityMethodInvestmentSalesProceedsInstallmentPaymentLatePayment |
Installment payments, including annual charges, received from the sale of the joint venture |  | 4.9 exh_EquityMethodInvestmentSalesProceedsInstallmentPayment
Remaining principal amount due from sale of joint venture | $ 22 exh_EquityMethodInvestmentExpectedNetSalesProceeds |
PIGAP II |  |
Ownership interest of each equity method investee |  |
Ownership Interest (as a percent) | 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = exh_PIGPIIMember |
El Furrial |  |
Ownership interest of each equity method investee |  |
Ownership Interest (as a percent) | 33.30%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = exh_ElFurrialMember |

X
- Definition The additional cash inflows expected to be received on disposal of an equity method investment. + References No definition available. + Details
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- Definition The cash inflows from installment payments received during the period on disposal of an equity method investment. + References No definition available. + Details
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- Definition The cash inflows from installment payments received as a late payment during the period on disposal of an equity method investment. + References No definition available. + Details
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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