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Goodwill rollforward (Details) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2014 | Mar. 31, 2013 | Dec. 31, 2013
Goodwill [Roll Forward] |  |  |  |  |  |
Balance as of beginning of period | $ 636,039,000 | [1] | $ 636,039,000 | [1] | $ 636,039,000 | [1]
Goodwill acquired during the year | 0 |  | 0 |  | 0 |
Balance as of end of period | 636,039,000 | [1] | 636,039,000 | [1] | 636,039,000 | [1]
Natural gas distribution [Member] |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Balance as of beginning of period | 345,736,000 |  | 345,736,000 |  | 345,736,000 |
Goodwill acquired during the year | 0 |  | 0 |  | 0 |
Balance as of end of period | 345,736,000 |  | 345,736,000 |  | 345,736,000 |
Pipeline and energy services [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Goodwill, impaired, accumulated impairment loss | 12,300,000 |  | 12,300,000 |  | 12,300,000 |
Goodwill [Roll Forward] |  |  |  |  |  |
Balance as of beginning of period | 9,737,000 | [1] | 9,737,000 | [1] | 9,737,000 | [1]
Goodwill acquired during the year | 0 |  | 0 |  | 0 |
Balance as of end of period | 9,737,000 | [1] | 9,737,000 | [1] | 9,737,000 | [1]
Construction materials and contracting [Member] |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Balance as of beginning of period | 176,290,000 |  | 176,290,000 |  | 176,290,000 |
Goodwill acquired during the year | 0 |  | 0 |  | 0 |
Balance as of end of period | 176,290,000 |  | 176,290,000 |  | 176,290,000 |
Construction services [Member] |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Balance as of beginning of period | 104,276,000 |  | 104,276,000 |  | 104,276,000 |
Goodwill acquired during the year | 0 |  | 0 |  | 0 |
Balance as of end of period | $ 104,276,000 |  | $ 104,276,000 |  | $ 104,276,000 |
[1] | Balance is presented net of accumulated impairment of $12.3 million at the pipeline and energy services segment, which occurred in prior periods.

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267 + Details
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- Definition Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a,h) -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267 + Details
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- Details
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- Details
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