QUARTERLY RESULTS OF OPERATIONS - UNAUDITED (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Operating Revenues	$ 146,172	$ 59,674	$ 66,536	$ 174,098	$ 129,010	$ 54,251	$ 59,177	$ 179,436	$ 446,480	$ 421,874	$ 412,449
Expenses:
Cost of Sales (excluding depreciation)	71,654	24,717	26,108	77,602	60,751	21,053	20,407	86,499	200,081	188,710	187,866
Operations and Maintenance Including Fixed Charges	39,486	33,249	33,871	38,659	33,877	32,953	33,597	35,102
Income Taxes	11,322	471	2,269	20,771	10,589	258	1,887	20,977	34,833	33,711	34,281
Energy and Other Taxes	2,530	1,052	1,277	3,003	2,485	1,167	1,479	3,169	7,862	8,300	10,291
Total Expenses	124,992	59,489	63,525	140,035	107,702	55,431	57,370	145,747
Other Income and Expense	773	764	810	1,450	(1,865)	1,703	1,430	1,349
Net Income	$ 21,953	$ 949	$ 3,821	$ 35,513	$ 19,443	$ 523	$ 3,237	$ 35,038	$ 62,236	$ 58,241	$ 52,889