Segment Information (details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting [Abstract]
Revenues	$ 87,199	$ 88,195	$ 513,754	$ 497,770
Depreciation and Amortization	19,938	18,737	59,236	56,474
Operating Income (Loss)	(5,077)	(3,787)	83,217	83,502
Net Income (Loss) Attributable to Parent	(8,733)	(8,233)	30,222	31,532
Payments to Acquire Property, Plant, and Equipment	34,063	31,232	86,552	86,287
Assets	2,833,524	2,805,913	2,833,524	2,805,913	2,970,911
Utility Margin [Abstract]
Cost of gas	32,227	33,655	245,708	235,156
Utility margin	50,134	47,050	250,223	239,151
Utility Segment [Member]
Segment Reporting [Abstract]
Revenues	82,361	80,705	495,931	474,307
Depreciation and Amortization	18,279	17,118	54,333	51,617
Operating Income (Loss)	(6,221)	(7,293)	78,971	72,372
Net Income (Loss) Attributable to Parent	(8,808)	(9,605)	29,416	27,083
Payments to Acquire Property, Plant, and Equipment	33,717	30,805	85,793	85,327
Assets	2,539,834	2,502,688	2,539,834	2,502,688	2,644,367
Gas Storage Segment [Member]
Segment Reporting [Abstract]
Revenues	4,782	7,434	17,655	23,295
Depreciation and Amortization	1,659	1,619	4,903	4,857
Operating Income (Loss)	926	3,556	3,994	11,138
Net Income (Loss) Attributable to Parent	2	1,407	472	4,495
Payments to Acquire Property, Plant, and Equipment	346	427	759	960
Assets	277,689	287,317	277,689	287,317	310,097
Other Segment [Member]
Segment Reporting [Abstract]
Revenues	56	56	168	168
Depreciation and Amortization	0	0	0	0
Operating Income (Loss)	218	(50)	252	(8)
Net Income (Loss) Attributable to Parent	73	(35)	334	(46)
Payments to Acquire Property, Plant, and Equipment	0	0	0	0
Assets	$ 16,001	$ 15,908	$ 16,001	$ 15,908	$ 16,447