Goodwill and Other Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Goodwill [Roll Forward]
Balance as of beginning of period	$ 634,633	[1]	$ 629,463	[1]
Goodwill Acquired During the Year	298	[2]	5,170	[3]
Balance as of end of period	634,931	[1]	634,633	[1]
Electric [Member]
Goodwill [Roll Forward]
Balance as of beginning of period	0		0
Goodwill Acquired During the Year	0	[2]	0	[3]
Balance as of end of period	0		0
Exploration and production [Member]
Goodwill [Roll Forward]
Balance as of beginning of period	0		0
Goodwill Acquired During the Year	0	[2]	0	[3]
Balance as of end of period	0		0
Natural gas distribution [Member]
Goodwill [Roll Forward]
Balance as of beginning of period	345,736		345,736
Goodwill Acquired During the Year	0	[2]	0	[3]
Balance as of end of period	345,736		345,736
Construction services [Member]
Goodwill [Roll Forward]
Balance as of beginning of period	102,870		100,127
Goodwill Acquired During the Year	298	[2]	2,743	[3]
Balance as of end of period	103,168		102,870
Pipeline and energy services [Member]
Goodwill [Roll Forward]
Balance as of beginning of period	9,737	[1]	7,857	[1]
Goodwill Acquired During the Year	0	[2]	1,880	[3]
Balance as of end of period	9,737	[1]	9,737	[1]
Accumulated impairment which occurred in prior periods	12,300		12,300
Construction materials and contracting [Member]
Goodwill [Roll Forward]
Balance as of beginning of period	176,290		175,743
Goodwill Acquired During the Year	0	[2]	547	[3]
Balance as of end of period	176,290		176,290
Other [Member]
Goodwill [Roll Forward]
Balance as of beginning of period	0		0
Goodwill Acquired During the Year	0	[2]	0	[3]
Balance as of end of period	$ 0		$ 0

[1] Balance is presented net of accumulated impairment of $12.3 million at the pipeline and energy services segment, which occurred in prior periods.

[2] Includes a purchase price adjustment that was not material related to an acquisition in a prior period.

[3] Includes purchase price adjustments that were not material related to acquisitions in a prior period.