Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Taxes and Interest Paid:
Income taxes paid	$ 10,916	$ 14,817	$ 15,984
Interest paid	22,305	21,822	22,236
Non-Cash Transactions:
Accrued payables for investment in utility plant	17,236	20,655	13,147
Property installed by developers and conveyed	5,395	3,284	800
GSWC
Taxes and Interest Paid:
Income taxes paid	8,437	1,541	16,500
Interest paid	22,078	21,797	22,184
Non-Cash Transactions:
Accrued payables for investment in utility plant	17,207	20,655	13,141
Property installed by developers and conveyed	$ 5,395	$ 3,284	$ 800