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Summary of Significant Accounting Policies (Details 2) (USD $) | Dec. 31, 2011 | Dec. 31, 2010
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Accounting Policies [Abstract] |  |
Aggregates held for resale | $ 78,518,000 | $ 79,894,000
Materials and supplies | 61,611,000 | 57,324,000
Natural gas in storage (current) | 36,578,000 | 34,557,000
Merchandise for resale | 32,165,000 | 30,182,000
Asphalt oil | 32,335,000 | 25,234,000
Other | 32,998,000 | 25,706,000
Inventories and natural gas in storage | 274,205,000 | 252,897,000
Natural gas in storage largely required to maintain pressure levels for normal operating purposes | $ 50,300,000 | $ 48,000,000

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