Regulatory Matters: (Details 5) (GSWC, USD $)			1 Months Ended	3 Months Ended	1 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Aug. 31, 2012 BVES General Rate Case	Mar. 31, 2013 BVES General Rate Case	Dec. 31, 2012 Renewables Portfolio Standard	Dec. 31, 2012 Renewables Portfolio Standard item	Mar. 31, 2013 Renewables Portfolio Standard	Mar. 31, 2013 Other regulatory assets, net	Dec. 31, 2012 Other regulatory assets, net
Regulatory matters:
Amount of retroactive ratemaking proposal included in DRA's recommendation to increase accumulated depreciation			$ 2,000,000
Net regulatory assets	185,229,000	176,015,000		2,200,000				40,280,000	40,332,000
Portion of deferred rate case costs required to be written off, if DRA prevails				50.00%
Provision for loss							$ 0
Agreement period to purchase renewable energy credits					10 years
Number of renewable energy credits that would be purchased						582,000