Regulatory Matters (Details 2) (USD $)	12 Months Ended						1 Months Ended	12 Months Ended		1 Months Ended				12 Months Ended	1 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 GSWC	Dec. 31, 2011 GSWC	Dec. 31, 2010 GSWC	Apr. 30, 2012 GSWC WRAM, net of MCBA	Dec. 31, 2012 GSWC WRAM, net of MCBA	Dec. 31, 2011 GSWC WRAM, net of MCBA	May 31, 2012 GSWC WRAM, net of MCBA Minimum	Apr. 30, 2012 GSWC WRAM, net of MCBA Minimum	May 31, 2012 GSWC WRAM, net of MCBA Maximum	Apr. 30, 2012 GSWC WRAM, net of MCBA Maximum	Dec. 31, 2012 GSWC WRAM, net of MCBA Maximum	May 31, 2012 GSWC WRAM	Dec. 31, 2012 GSWC WRAM	Dec. 31, 2012 GSWC Modified Cost Balancing Account	Dec. 31, 2012 GSWC Base revenue requirement adjustment mechanism	Dec. 31, 2011 GSWC Base revenue requirement adjustment mechanism
Regulatory matters:
Commercial paper, term								90 days
Amount billed to customers as surcharges								$ 19,600,000
Under-collections recorded	(11,709,000)	(18,748,000)	(20,622,000)	(11,709,000)	(18,748,000)	(20,622,000)		21,100,000										2,300,000
Under (over) collection				176,015,000	179,957,000			42,574,000	39,112,000							61,900,000	(19,300,000)	6,833,000	4,053,000
Alternative revenue program														24 months
Recovery periods										12 months		36 months			18 months
Under-collection balances as a percentage of adopted annual revenues							15.00%
Recovery period for under-collection balances that are up to 15% of adopted annual revenues													18 months
Recovery period for under-collection balances greater than 15% of adopted annual revenues											19 months		36 months
Modified recovery period												18 months
Annual surcharges as a percentage of the last authorized revenue requirement							10.00%
Period of surcharge approved																		36 months
Increase in revenue requirement recoverable through surcharges collected																		$ 1,600,000