Segment Information (details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Segment Reporting [Abstract]
Gross Profit	$ 49,915	$ 47,783	$ 259,262	$ 249,523
Depreciation and Amortization	18,281	17,449	54,330	52,304
Operating Income (Loss)	(4,796)	(5,552)	85,709	84,963
Net Income (Loss) Attributable to Parent	(10,558)	(8,312)	31,458	34,654
Assets	2,690,368	2,567,840	2,690,368	2,567,840	2,746,574
Utility Segment [Member]
Segment Reporting [Abstract]
Gross Profit	42,331	41,034	236,921	230,244
Depreciation and Amortization	16,661	15,875	49,477	47,735
Operating Income (Loss)	(8,439)	(8,029)	76,072	77,762
Net Income (Loss) Attributable to Parent	(11,853)	(9,518)	28,250	31,702
Assets	2,386,879	2,291,531	2,386,879	2,291,531	2,435,888
Gas Storage Segment [Member]
Segment Reporting [Abstract]
Gross Profit	7,544	6,710	22,219	19,211
Depreciation and Amortization	1,620	1,574	4,853	4,569
Operating Income (Loss)	3,624	2,458	9,567	7,191
Net Income (Loss) Attributable to Parent	1,255	1,160	3,185	3,163
Assets	287,687	253,478	287,687	253,478	294,637
Other Segment [Member]
Segment Reporting [Abstract]
Gross Profit	40	39	122	68
Depreciation and Amortization	0	0	0	0
Operating Income (Loss)	19	19	70	10
Net Income (Loss) Attributable to Parent	40	46	23	(211)
Assets	$ 15,802	$ 22,831	$ 15,802	$ 22,831	$ 16,049