SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 town segment	Dec. 31, 2011	Dec. 31, 2010
SEGMENT INFORMATION
Number of business segments									3
Number of towns to which water service is provided									3
Statement of Income Information, balance sheet information and capital expenditures of business segments
Revenues	$ 129,119	$ 159,202	$ 131,632	$ 137,144	$ 132,765	$ 164,284	$ 129,093	$ 150,728	$ 557,097	$ 576,870	$ 541,276
Depreciation and amortization									60,447	63,537	58,656
Federal and state income taxes									34,159	34,298	30,533
Operating income	19,367	35,282	20,762	20,810	19,502	36,450	19,134	21,848	96,221	96,934	80,495
Interest income									972	555	176
Interest expense									41,467	41,520	42,347
Income from AFUDC (debt and equity)									1,928	512	10,174
Income from continuing operations	9,627	25,542	10,708	9,804	8,690	25,184	9,175	11,922	55,681	54,971	47,396
Capital Expenditures									146,287	101,177	108,157
Total assets	2,126,369				2,021,835				2,126,369	2,021,835
Goodwill	39,492				39,492				39,492	39,492
Electric
Statement of Income Information, balance sheet information and capital expenditures of business segments
Revenues									510,653	524,276	484,715
Depreciation and amortization									55,312	58,236	53,983
Federal and state income taxes									32,266	31,643	27,925
Operating income									89,445	88,590	72,528
Interest income									946	554	198
Interest expense									37,866	37,860	38,798
Income from AFUDC (debt and equity)									1,918	509	10,155
Income from continuing operations									52,631	50,670	43,187
Capital Expenditures									140,117	93,499	100,146
Total assets	2,034,399				1,931,320				2,034,399	1,931,320
Gas
Statement of Income Information, balance sheet information and capital expenditures of business segments
Revenues									39,849	46,430	50,885
Depreciation and amortization									3,598	3,494	3,032
Federal and state income taxes									789	1,676	1,620
Operating income									5,005	6,514	6,327
Interest income									323	259	403
Interest expense									3,905	3,910	3,941
Income from AFUDC (debt and equity)									10	3	19
Income from continuing operations									1,256	2,709	2,602
Capital Expenditures									3,571	4,122	5,242
Total assets	148,814				145,897				148,814	145,897
Other
Statement of Income Information, balance sheet information and capital expenditures of business segments
Revenues									7,187	6,756	6,268
Depreciation and amortization									1,537	1,807	1,641
Federal and state income taxes									1,104	979	988
Operating income									1,771	1,830	1,640
Interest income									7
Interest expense										8	33
Income from continuing operations									1,794	1,592	1,607
Capital Expenditures									2,599	3,556	2,769
Total assets	28,871				26,038				28,871	26,038
Eliminations
Statement of Income Information, balance sheet information and capital expenditures of business segments
Revenues									(592)	(592)	(592)
Interest income									(304)	(258)	(425)
Interest expense									(304)	(258)	(425)
Total assets	$ (85,715)				$ (81,420)				$ (85,715)	$ (81,420)