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Inventories and natural gas in storage (Details) (USD $) | Sep. 30, 2014 | Dec. 31, 2013 | Sep. 30, 2013
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Inventory Disclosure [Abstract] |  |  |
Aggregates held for resale | $ 106,623,000 | $ 101,568,000 | $ 104,784,000
Asphalt oil | 33,551,000 | 38,099,000 | 43,078,000
Materials and supplies | 71,515,000 | 69,808,000 | 71,370,000
Merchandise for resale | 24,566,000 | 21,720,000 | 23,713,000
Natural gas in storage (current) | 29,979,000 | 16,417,000 | 37,689,000
Other | 36,471,000 | 34,779,000 | 33,937,000
Total | 302,705,000 | 282,391,000 | 314,571,000
Natural gas in storage noncurrent | $ 47,400,000 | $ 48,300,000 | $ 48,600,000

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- Definition Aggregated amount of asphalt oil inventory. This amount is net of valuation reserves and adjustments. + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of natural gas in storage, which is a mixture of gases (liquefied or otherwise), used for fuel and manufacturing purposes, which is ready for sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(a)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -Article 5 + Details
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- Definition Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Subparagraph a -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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