Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Plant and property, at original cost:
Electric	$ 2,432,098	$ 2,420,824
Gas	80,112	79,364
Other	41,447	41,394
Construction work in progress	151,023	112,097
Total plant and property, Gross	2,704,680	2,653,679
Accumulated depreciation and amortization	758,765	743,407
Total plant and property, Net	1,945,915	1,910,272
Current assets:
Cash and cash equivalents	2,661	2,105
Restricted cash	4,726	4,726
Accounts receivable - trade, net of allowance of $1,355 and $1,021 respectively	52,755	45,444
Accrued unbilled revenues	16,595	25,945
Accounts receivable - other	30,047	41,256
Fuel, materials and supplies	56,167	57,799
Prepaid expenses and other	31,789	27,879
Unrealized gain in fair value of derivative contracts	1,466	3,901
Regulatory assets	8,650	10,752
Total current assets	204,856	219,807
Noncurrent assets and deferred charges:
Regulatory assets	204,947	209,717
Goodwill	39,492	39,492
Unamortized debt issuance costs	8,672	8,821
Other	3,697	2,147
Total noncurrent assets and deferred charges	256,808	260,177
Total Assets	2,407,579	2,390,256
Capitalization and liabilities
Common stock, $1 par value, 43,572,712 and 43,479,186 shares issued and outstanding, respectively	43,573	43,479
Capital in excess of par value	652,290	649,543
Retained earnings	93,595	90,276
Total common stockholders' equity	789,458	783,298
Long-term debt (net of current portion):
Obligations under capital lease	3,799	3,875
First mortgage bonds and secured debt	697,624	697,615
Unsecured debt	101,703	101,699
Total long-term debt	803,126	803,189
Total long-term debt and common stockholders' equity	1,592,584	1,586,487
Current liabilities:
Accounts payable and accrued liabilities	55,342	83,420
Current maturities of long-term debt	320	292
Short-term debt	53,000	44,000
Regulatory liabilities	5,559	7,898
Customer deposits	13,920	13,747
Interest accrued	14,671	6,565
Unrealized loss in fair value of derivative contracts	6,685	6,469
Taxes accrued	10,260	3,380
Other current liabilities	408	356
Total current liabilities	160,165	166,127
Commitments and contingencies (Note 7)
Noncurrent liabilities and deferred credits:
Regulatory liabilities	133,303	128,471
Deferred income taxes	390,455	377,452
Unamortized investment tax credits	18,361	18,367
Pension and other postretirement benefit obligations	93,165	93,863
Unrealized loss in fair value of derivative contracts	4,488	3,243
Other	15,058	16,246
Total noncurrent liabilities and deferred credits	654,830	637,642
Total Capitalization and Liabilities	$ 2,407,579	$ 2,390,256