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Inventories and natural gas in storage (Details) (USD $) | Jun. 30, 2011 | Dec. 31, 2010 | Jun. 30, 2010
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Inventories [Abstract] |  |  |
Aggregates held for resale | $ 82,936,000 | $ 79,894,000 | $ 83,535,000
Materials and supplies | 65,363,000 | 57,324,000 | 62,070,000
Natural gas in storage (current) | 11,993,000 | 34,557,000 | 14,269,000
Merchandise for resale | 33,435,000 | 30,182,000 | 28,438,000
Asphalt oil | 55,729,000 | 25,234,000 | 51,956,000
Other | 27,871,000 | 25,706,000 | 19,895,000
Total | 277,327,000 | 252,897,000 | 260,163,000
Natural gas in storage largely required to maintain pressure levels for normal operating purposes | $ 47,200,000 | $ 48,000,000 | $ 59,300,000

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