Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in allowance for doubtful accounts
Balance at beginning of year	$ 764	$ 944	$ 892
Provision charged to expense	989	619	870
Accounts written off, net of recoveries	712	799	818
Balance at end of year	1,041	764	944
Components of allowance for doubtful accounts
Allowance for doubtful accounts related to accounts receivable-customer				$ 806	$ 702	$ 790
Allowance for doubtful accounts related to other accounts receivable				235	62	154
Total allowance for doubtful accounts	764	944	892	1,041	764	944
GSWC
Changes in allowance for doubtful accounts
Balance at beginning of year	761	919	892
Provision charged to expense	816	627	845
Accounts written off, net of recoveries	712	785	818
Balance at end of year	865	761	919
Components of allowance for doubtful accounts
Allowance for doubtful accounts related to accounts receivable-customer				806	702	790
Allowance for doubtful accounts related to other accounts receivable				59	59	129
Total allowance for doubtful accounts	$ 761	$ 919	$ 892	$ 865	$ 761	$ 919