Summary of Significant Accounting Policies (Details 2) (USD $)	Dec. 31, 2011	Dec. 31, 2010
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