Consolidated Statements of Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Operating revenues:
Gross operating revenues	$ 106,569	$ 161,197	$ 424,063	$ 484,285
Less: Cost of sales	34,512	90,122	204,283	270,747
Revenue taxes	2,578	3,843	10,433	11,798
Net operating revenues	69,479	67,232	209,347	201,740
Operating expenses:
Operations and maintenance	32,124	30,374	66,540	61,546
General taxes	7,417	6,659	16,253	14,824
Depreciation and amortization	18,099	17,546	36,049	34,855
Total operating expenses	57,640	54,579	118,842	111,225
Income from operations	11,839	12,653	90,505	90,515
Other income and expense - net	921	1,122	1,926	2,336
Interest expense - net	10,464	10,266	21,655	20,715
Income before income taxes	2,296	3,509	70,776	72,136
Income tax expense	887	1,316	28,760	29,170
Net income	1,409	2,193	42,016	42,966
Other comprehensive income
Amortization of non-qualified employee benefit plan liability, net of taxes of $109 and $96 for the three months and $217 and $192 for the six months ended June 30, 2012 and 2011, respectively	166	146	332	292
Comprehensive income	$ 1,575	$ 2,339	$ 42,348	$ 43,258
Average common shares outstanding:
Basic	26,812	26,673	26,797	26,671
Diluted	26,896	26,727	26,879	26,725
Earnings per share of common stock
Earnings per share of common stock - basic	$ 0.05	$ 0.08	$ 1.57	$ 1.61
Earnings per share of common stock - diluted	$ 0.05	$ 0.08	$ 1.56	$ 1.61
Dividends declared per share of common stock	$ 0.445	$ 0.435	$ 0.890	$ 0.870