Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Plant and property, at original cost:
Electric	$ 2,420,824	$ 2,219,605
Gas	79,364	72,834
Other	41,394	39,902
Construction work in progress	112,097	152,330
Total plant and property, Gross	2,653,679	2,484,671
Accumulated depreciation and amortization	743,407	732,737
Total plant and property, Net	1,910,272	1,751,934
Current assets:
Cash and cash equivalents	2,105	3,475
Restricted cash	4,726	2,872
Accounts receivable - trade, net of allowance of $1,021 and $1,025, respectively	45,444	50,137
Accrued unbilled revenues	25,945	26,694
Accounts receivable - other	41,256	13,101
Fuel, materials and supplies	57,799	48,811
Prepaid expenses and other	27,879	15,954
Unrealized gain in fair value of derivative contracts	3,901	2,469
Regulatory assets	10,752	7,743
Total current assets	219,807	171,256
Noncurrent assets and deferred charges:
Regulatory assets	209,717	169,333
Goodwill	39,492	39,492
Unamortized debt issuance costs	8,821	8,826
Unrealized gain in fair value of derivative contracts		41
Other	2,147	4,163
Total noncurrent assets and deferred charges	260,177	221,855
Total Assets	2,390,256	2,145,045
Capitalization and liabilities
Common stock, $1 par value, 100,000,000 shares authorized, 43,479,186 and 43,044,185 shares issued and outstanding, respectively	43,479	43,044
Capital in excess of par value	649,543	639,525
Retained earnings	90,276	67,554
Total common stockholders' equity	783,298	750,123
Long-term debt (net of current portion):
Obligations under capital lease	3,875	4,167
First mortgage bonds and secured debt	697,615	637,578
Unsecured debt	101,699	101,683
Total long-term debt	803,189	743,428
Total long-term debt and common stockholders' equity	1,586,487	1,493,551
Current liabilities:
Accounts payable and accrued liabilities	83,420	71,375
Current maturities of long-term debt	292	274
Short-term debt	44,000	4,000
Regulatory liabilities	7,898	5,681
Customer deposits	13,747	12,543
Interest accrued	6,565	6,352
Unrealized loss in fair value of derivative contracts	6,469	1,889
Taxes accrued	3,380	3,386
Other current liabilities	356	299
Total current liabilities	166,127	105,799
Commitments and contingencies (Note 11)
Noncurrent liabilities and deferred credits:
Regulatory liabilities	128,471	132,012
Deferred income taxes	377,452	324,266
Unamortized investment tax credits	18,367	18,431
Pension and other postretirement benefit obligations	93,863	51,405
Unrealized loss in fair value of derivative contracts	3,243	2,799
Other	16,246	16,782
Total noncurrent liabilities and deferred credits	637,642	545,695
Total capitalization and liabilities	$ 2,390,256	$ 2,145,045