Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Utility plant:
Land	$ 42,023	$ 37,703
Depreciable plant and equipment	1,903,365	1,807,569
Construction work in progress	132,362	98,623
Intangible assets	18,613	16,486
Total utility plant	2,096,363	1,960,381
Less accumulated depreciation and amortization	(639,307)	(579,262)
Net utility plant	1,457,056	1,381,119
Current assets:
Cash and cash equivalents	38,790	27,203
Receivables: net of allowance for doubtful accounts of $714 and $669, respectively
Customers	29,958	28,418
Regulatory balancing accounts	34,020	21,680
Other	11,943	6,422
Unbilled revenue	15,394	15,068
Materials and supplies at weighted average cost	5,874	5,913
Taxes, prepaid expenses, and other assets	10,585	9,184
Total current assets	146,564	113,888
Other assets:
Regulatory assets	344,419	319,898
Unamortized debt premium and expense	5,591	6,071
Goodwill	2,615	2,615
Other	39,679	30,996
Total other assets	392,304	359,580
Total assets	1,995,924	1,854,587
Capitalization:
Common stock, $0.01 par value; 68,000 shares authorized, 41,908 and 41,817, outstanding in 2012 and 2011, respectively	419	418
Additional paid-in capital	221,013	219,572
Retained earnings	252,280	229,839
Total common stockholders' equity	473,712	449,829
Long-term debt, less current maturities	434,467	481,632
Total capitalization	908,179	931,461
Current liabilities:
Current maturities of long-term debt	46,783	6,533
Short-term borrowings	89,475	47,140
Accounts payable	47,199	48,923
Regulatory balancing accounts	5,018	2,655
Accrued other taxes	3,379	3,942
Accrued interest	4,705	4,756
Other accrued liabilities	46,508	37,926
Total current liabilities	243,067	151,875
Unamortized investment tax credits	2,180	2,254
Deferred income taxes	158,846	116,368
Regulatory liabilities	35,720	28,037
Pension and postretirement benefits other than pension	244,901	232,110
Advances for construction	187,584	187,278
Contributions in aid of construction	158,574	154,191
Other long-term liabilities	56,873	51,013
Commitments and contingencies
Total capitalization and liabilities	$ 1,995,924	$ 1,854,587