Supplemental Cash Flow Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Taxes and Interest Paid:
Income taxes paid	$ 19,411	$ 31,842	$ 22,287
Interest paid	22,495	22,671	21,632
Non-Cash Transactions:
Accrued payables for investment in utility plant	12,113	13,717	9,046
Property installed by developers and conveyed	2,069	1,264	3,471
GSWC
Taxes and Interest Paid:
Income taxes paid	11,027	25,810	16,310
Interest paid	22,495	22,463	21,016
Non-Cash Transactions:
Accrued payables for investment in utility plant	12,113	13,717	9,046
Property installed by developers and conveyed	$ 2,069	$ 1,264	$ 3,471