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Inventories and natural gas in storage (Details) (USD $) | Sep. 30, 2011 | Dec. 31, 2010 | Sep. 30, 2010
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Inventories [Abstract] |  |  |
Aggregates held for resale | $ 80,868,000 | $ 79,894,000 | $ 82,622,000
Materials and supplies | 64,988,000 | 57,324,000 | 62,273,000
Natural gas in storage (current) | 39,629,000 | 34,557,000 | 40,133,000
Merchandise for resale | 30,974,000 | 30,182,000 | 29,566,000
Asphalt oil | 26,851,000 | 25,234,000 | 24,341,000
Other | 26,259,000 | 25,706,000 | 22,745,000
Total | 269,569,000 | 252,897,000 | 261,680,000
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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