Allowance for Doubtful Accounts (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in allowance for doubtful accounts
Balance at beginning of year	$ 1,048	$ 1,051	$ 1,158
Provision charged to expense	1,710	938	1,041
Accounts written off, net of recoveries	(1,530)	(941)	(1,148)
Balance at end of year	1,228	1,048	1,051
Components of allowance for doubtful accounts
Allowance for doubtful accounts related to accounts receivable-customer	797	715	670
Allowance for doubtful accounts related to receivable from U.S. government	8		43
Allowance for doubtful accounts related to other accounts receivable	423	333	338
Total allowance for doubtful accounts	1,228	1,048	1,051
GSWC
Changes in allowance for doubtful accounts
Balance at beginning of year	1,005	1,005	1,088
Provision charged to expense	1,668	859	1,041
Accounts written off, net of recoveries	(1,496)	(859)	(1,124)
Balance at end of year	1,177	1,005	1,005
Components of allowance for doubtful accounts
Allowance for doubtful accounts related to accounts receivable-customer	797	715	670
Allowance for doubtful accounts related to other accounts receivable	380	290	335
Total allowance for doubtful accounts	$ 1,177	$ 1,005	$ 1,005