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Reportable Segments and Geographic Information (Details Textual) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 Segment | Dec. 31, 2010 | Dec. 31, 2009
Reportable Segments (Textual) [Abstract] |  |  |
Number of business segments | 4 |  |
Percentage of total revenue accounted for threshold limit of sales revenue | 10.00% |  |
Major customer, Amount | $ 0 | $ 0 | $ 0

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- Definition Number of business segments. + References No definition available. + Details
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Namespace Prefix: | exh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage of threshold limit of sales revenue. + References No definition available. + Details
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Namespace Prefix: | exh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
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Namespace Prefix: | exh_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of revenue generated from a single external customer that accounts for 10 percent or more of an entity's revenues. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 131 -Paragraph 39 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 42 -URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9054-108599 + Details
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Namespace Prefix: | us-gaap_
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Period Type: | duration