Investment in ATC (Details-1) (USD $)	6 Months Ended				6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 ATC [Member]	Dec. 31, 2011 ATC [Member]	Jun. 30, 2012 ATC [Member] Mge Transco [Member]	Jun. 30, 2011 ATC [Member] Mge Transco [Member]
Equity method investments [Line Items]
Equity earnings from investment in ATC	$ 4,484,000	$ 4,267,000			$ 4,500,000	$ 4,300,000
Dividend income from ATC	3,494,000	3,327,000			3,500,000	3,300,000
Contributions to ATC					900,000	600,000
Investment in ATC			$ 58,900,000	$ 57,000,000