SEGMENT INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011 town segment	Dec. 31, 2010	Dec. 31, 2009
SEGMENT INFORMATION
Number of business segments									3
Number of towns to which water service is provided									3
Statement of Operations Information, balance sheet information and capital expenditures of business segments
Revenues	$ 132,765	$ 164,284	$ 129,093	$ 150,728	$ 132,815	$ 154,086	$ 114,482	$ 139,893	$ 576,870	$ 541,276	$ 497,168
Depreciation and amortization									63,537	58,656	51,494
Federal and state income taxes									34,298	30,533	19,882
Operating income	19,502	36,450	19,134	21,848	18,265	31,873	14,279	16,078	96,934	80,495	74,495
Interest income									555	176	217
Interest expense									41,520	42,347	46,778
Income from AFUDC (debt and equity)									512	10,174	14,133
Income from continuing operations	8,690	25,184	9,175	11,922	8,460	22,981	7,369	8,586	54,971	47,396	41,296
Capital Expenditures									101,177	108,157	148,804
Total assets	2,021,835				1,921,311				2,021,835	1,921,311
Goodwill	39,492				39,492				39,492	39,492
Electric
Statement of Operations Information, balance sheet information and capital expenditures of business segments
Revenues									524,276	484,715	434,897
Depreciation and amortization									58,236	53,983	48,036
Federal and state income taxes									31,643	27,925	18,484
Operating income									88,590	72,528	68,414
Interest income									554	198	225
Interest expense									37,860	38,798	43,173
Income from AFUDC (debt and equity)									509	10,155	14,131
Income from continuing operations									50,670	43,187	39,078
Capital Expenditures									93,499	100,146	145,287
Total assets	1,931,320				1,837,910				1,931,320	1,837,910
Gas
Statement of Operations Information, balance sheet information and capital expenditures of business segments
Revenues									46,430	50,885	57,314
Depreciation and amortization									3,494	3,032	2,015
Federal and state income taxes									1,676	1,620	572
Operating income									6,514	6,327	4,634
Interest income									259	403	403
Interest expense									3,910	3,941	3,959
Income from AFUDC (debt and equity)									3	19	2
Income from continuing operations									2,709	2,602	874
Capital Expenditures									4,122	5,242	2,256
Total assets	145,897				139,532				145,897	139,532
Other.
Statement of Operations Information, balance sheet information and capital expenditures of business segments
Revenues									6,756	6,268	5,562
Depreciation and amortization									1,807	1,641	1,443
Federal and state income taxes									979	988	826
Operating income									1,830	1,640	1,447
Interest expense									8	33	57
Income from continuing operations									1,592	1,607	1,344
Capital Expenditures									3,556	2,769	1,261
Total assets	26,038				23,163				26,038	23,163
Eliminations
Statement of Operations Information, balance sheet information and capital expenditures of business segments
Revenues									(592)	(592)	(605)
Interest income									(258)	(425)	(411)
Interest expense									(258)	(425)	(411)
Total assets	$ (81,420)				$ (79,294)				$ (81,420)	$ (79,294)