Utility Plant and Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Utility plant utilized in continuing operations by major asset class
Total	$ 1,314,283	$ 1,268,112
Less - accumulated depreciation	(442,316)	(413,836)
Construction work in progress	45,824	42,224
Net utility plant	917,791	896,500	854,956
Water
Utility plant utilized in continuing operations by major asset class
Total	1,236,630	1,194,287
Water | Land
Utility plant utilized in continuing operations by major asset class
Total	15,357	15,215
Water | Intangible assets
Utility plant utilized in continuing operations by major asset class
Total	33,750	33,122
Water | Source of water supply
Utility plant utilized in continuing operations by major asset class
Total	72,020	69,020
Water | Pumping
Utility plant utilized in continuing operations by major asset class
Total	142,586	138,912
Water | Water treatment
Utility plant utilized in continuing operations by major asset class
Total	63,738	65,034
Water | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total	796,973	768,405
Water | General
Utility plant utilized in continuing operations by major asset class
Total	112,206	104,579
Electric
Utility plant utilized in continuing operations by major asset class
Total	77,653	73,825
Electric | Intangible assets
Utility plant utilized in continuing operations by major asset class
Total	1,200	1,200
Electric | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total	56,757	52,651
Electric | Generation
Utility plant utilized in continuing operations by major asset class
Total	12,547	12,547
Electric | General
Utility plant utilized in continuing operations by major asset class
Total	8,349	8,627
GSWC
Utility plant utilized in continuing operations by major asset class
Total	1,305,366	1,261,381
Less - accumulated depreciation	(437,949)	(410,644)
Construction work in progress	45,720	41,208
Net utility plant	913,137	891,945
GSWC | Water
Utility plant utilized in continuing operations by major asset class
Total	1,227,713	1,187,556
Net utility plant	871,756	852,264	813,942
GSWC | Water | Land
Utility plant utilized in continuing operations by major asset class
Total	15,357	15,215
GSWC | Water | Intangible assets
Utility plant utilized in continuing operations by major asset class
Total	33,731	33,103
GSWC | Water | Source of water supply
Utility plant utilized in continuing operations by major asset class
Total	72,020	69,020
GSWC | Water | Pumping
Utility plant utilized in continuing operations by major asset class
Total	142,586	138,912
GSWC | Water | Water treatment
Utility plant utilized in continuing operations by major asset class
Total	63,738	65,034
GSWC | Water | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total	796,973	768,405
GSWC | Water | General
Utility plant utilized in continuing operations by major asset class
Total	103,308	97,867
GSWC | Electric
Utility plant utilized in continuing operations by major asset class
Total	77,653	73,825
Net utility plant	41,381	39,681	37,425
GSWC | Electric | Transmission and distribution
Utility plant utilized in continuing operations by major asset class
Total	56,757	52,651
GSWC | Electric | Generation
Utility plant utilized in continuing operations by major asset class
Total	12,547	12,547
GSWC | Electric | General
Utility plant utilized in continuing operations by major asset class
Total	$ 8,349	$ 8,627