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Inventories and natural gas in storage (Details) (USD $) | Sep. 30, 2012 | Dec. 31, 2011 | Sep. 30, 2011
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Inventories and natural gas in storage [Abstract] |  |  |
Aggregates held for resale | $ 88,632,000 | $ 78,518,000 | $ 80,868,000
Asphalt oil | 47,084,000 | 32,335,000 | 26,851,000
Materials and supplies | 75,551,000 | 61,611,000 | 64,988,000
Merchandise for resale | 30,827,000 | 32,165,000 | 30,974,000
Natural gas in storage (current) | 41,091,000 | 36,578,000 | 39,629,000
Other | 32,582,000 | 32,998,000 | 26,259,000
Total | 315,767,000 | 274,205,000 | 269,569,000
Natural gas in storage noncurrent | $ 50,300,000 | $ 50,300,000 | $ 47,200,000

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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 largely represents the cost of gas required to maintain pressure levels for normal operating purposes, and deemed to be noncurrent asset. + 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 last-in first-out (LIFO) and valuation reserves of merchandise or goods held by the entity that are readily available for sale. + 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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- Definition Carrying amount (lower of cost or market) as of the balance sheet date of inventories less all valuation and other allowances. Excludes noncurrent inventory balances (expected to remain on hand past one year or one operating cycle, if longer). + 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 FASB -Name Accounting Standards Codification -Topic 330 -SubTopic 10 -Section 35 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6386567&loc=d3e3927-108312 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6361293&loc=d3e6676-107765 + Details
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- Definition Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed. + 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)(4),(5)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Carrying amount, net of valuation reserves and allowances, as of the balance sheet date of inventories not otherwise specified in the taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 330 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.BB) -URI http://asc.fasb.org/extlink&oid=6386940&loc=d3e100047-122729 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 6 -Article 5 Reference 3: 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) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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