Regulatory Matters 9 (Details) - GSWC renewable_energy in Thousands, $ in Thousands	1 Months Ended
	Dec. 31, 2012 renewable_energy	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Regulatory matters:
Net regulatory assets | $		$ 146,281	$ 132,696
Renewables Portfolio Standard
Regulatory matters:
Agreement period to purchase renewable energy credits	10 years
Number of renewable energy credits that would be purchased | renewable_energy	582