Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting [Abstract]
Revenues	$ 93,128	$ 87,199	$ 493,073	$ 513,754
Depreciation and Amortization	20,342	19,938	60,683	59,236
Operating Income (Loss)	(1,873)	(5,077)	64,042	83,217
Net Income (Loss) Attributable to Parent	(6,685)	(8,733)	23,998	30,222
Payments to Acquire Property, Plant, and Equipment	28,851	34,063	86,923	86,552
Assets	2,978,365	2,833,524	2,978,365	2,833,524	$ 3,064,945
Utility Margin [Abstract]
Utility operating revenues	93,128	87,199	493,073	513,754
Less: Utility cost of gas	35,856	32,227	223,737	245,708
Operating Segments [Member] | Utility Segment [Member]
Segment Reporting [Abstract]
Revenues	87,475	82,361	476,672	495,931
Depreciation and Amortization	18,721	18,279	55,798	54,333
Operating Income (Loss)	(4,088)	(6,221)	59,955	78,971
Net Income (Loss) Attributable to Parent	(7,529)	(8,808)	23,051	29,416
Payments to Acquire Property, Plant, and Equipment	28,325	33,717	84,598	85,793
Assets	2,693,953	2,539,834	2,693,953	2,539,834	2,775,011
Utility Margin [Abstract]
Utility operating revenues	87,475	82,361	476,672	495,931
Less: Utility cost of gas	35,856	32,227	223,737	245,708
Utility margin	51,619	50,134	252,935	250,223
Operating Segments [Member] | Gas Storage Segment [Member]
Segment Reporting [Abstract]
Revenues	5,596	4,782	16,232	17,655
Depreciation and Amortization	1,621	1,659	4,885	4,903
Operating Income (Loss)	2,204	926	3,998	3,994
Net Income (Loss) Attributable to Parent	799	2	827	472
Payments to Acquire Property, Plant, and Equipment	526	346	2,325	759
Assets	269,289	277,689	269,289	277,689	273,813
Utility Margin [Abstract]
Utility operating revenues	5,596	4,782	16,232	17,655
Operating Segments [Member] | Other Segment [Member]
Segment Reporting [Abstract]
Revenues	57	56	169	168
Depreciation and Amortization	0	0	0	0
Operating Income (Loss)	11	218	89	252
Net Income (Loss) Attributable to Parent	45	73	120	334
Payments to Acquire Property, Plant, and Equipment	0	0	0	0
Assets	15,123	16,001	15,123	16,001	$ 16,121
Utility Margin [Abstract]
Utility operating revenues	$ 57	$ 56	$ 169	$ 168