CONSOLIDATED BALANCE SHEETS (UNAUDITED) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 1,368	$ 4,459
Accounts receivable, net	49,584	50,706
Accrued unbilled revenues	39,210	49,138
Inventories	17,773	19,685
Regulatory assets	15,197	12,048
Prepaid taxes	22,490	24,688
Deferred income taxes	2,445	0
Prepayments and other	2,251	4,394
Total current assets	150,318	165,118
Property, plant and equipment, net	1,343,713	1,298,236
Other assets
Regulatory assets	236,085	240,459
Other investments	3,461	3,232
Other	3,662	4,040
Total other assets	243,208	247,731
Total assets	1,737,239	1,711,085
Current liabilities
Current portion of long-term debt	103	1,246
Short-term debt	2,000	39,000
Notes payable to affiliates	470	550
Accounts payable	26,838	30,723
Accounts payable to affiliates	29,461	31,556
Dividends payable to parent	7,757	7,667
Regulatory liabilities	7,718	6,086
Environmental liabilities	17,561	23,427
Accrued interest	7,470	7,304
Other	11,577	11,794
Total current liabilities	110,955	159,353
Deferred credits and other liabilities
Deferred income taxes	280,604	261,800
Deferred investment tax credits	9,294	8,911
Regulatory liabilities	125,016	123,746
Environmental liabilities	87,170	84,655
Customer advances	16,449	15,631
Pension and employee benefit obligations	53,394	63,643
Other	8,672	8,923
Total deferred credits and other liabilities	580,599	567,309
Commitments and contingencies
Capitalization
Long-term debt	468,494	467,317
Common stock — 1,000,000 shares authorized of $100 par value; 933,000 shares outstanding at June 30, 2013 and Dec. 31, 2012, respectively	93,300	93,300
Additional paid in capital	234,961	189,867
Retained earnings	249,330	234,376
Accumulated other comprehensive loss	(400)	(437)
Total common stockholder’s equity	577,191	517,106
Total liabilities and equity	$ 1,737,239	$ 1,711,085