Business Segment Data (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 Information [Line Items]
Operating Income	$ 10,843	$ 8,516	$ 21,930	$ 20,022
Net Income	6,138	5,143	11,670	11,398
Capital Expenditures			17,886	17,647
Assets	548,050		548,050		537,536
Regulated
Segment Reporting Information [Line Items]
Revenues	29,085	26,262	74,385	70,935
Operating Income	10,417	8,241	20,798	18,893
Net Income	5,926	4,630	11,070	10,375
Capital Expenditures	5,222	6,389	17,564	17,245
Assets	546,879		546,879		539,947
Non - Regulated
Segment Reporting Information [Line Items]
Revenues	3,441	2,605	9,288	8,220
Operating Income	426	275	1,132	1,129
Net Income	212	513	600	1,023
Capital Expenditures	83	219	322	402
Assets	11,321		11,321		10,325
Inter-segment Elimination
Segment Reporting Information [Line Items]
Revenues	(173)	(196)	(373)	(386)
Assets	(10,150)		(10,150)		(12,736)
Consolidated
Segment Reporting Information [Line Items]
Number of Reportable Segments			2
Revenues	32,353	28,671	83,300	78,769
Operating Income	10,843	8,516	21,930	20,022
Net Income	6,138	5,143	11,670	11,398
Capital Expenditures	5,312	6,608	17,886	17,647
Assets	$ 548,050		$ 548,050		$ 537,536