Black Hills Power 10-K 27 Feb 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information Document (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Jan. 31, 2014
Entity Information [Line Items]	'	'
Entity Registrant Name	'BLACK HILLS POWER INC	'
Entity Central Index Key	'0000012400	'
Document Type	'10-K	'
Document Period End Date	31-Dec-13	'
Amendment Flag	'false	'
Document Fiscal Year End Focus	'2013	'
Document Fiscal Period Focus	'FY	'
Current Fiscal Year End Date	'--12-31	'
Entity Current Reporting Status	'Yes	'
Entity Filer Category	'Non-accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	23,416,396
Entity Well-known Seasoned Issuer	'Yes	'
Entity Voluntary Filers	'No	'
Entity Public Float	$0	'

Statements_of_Income

Statements of Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenue	$254,027	$243,309	$245,631
Operating expenses:	'	'	'
Fuel and purchased power	89,437	87,519	93,222
Operations and maintenance	68,857	65,835	66,683
Gain on sale of operating assets	0	0	-768
Depreciation and amortization	28,125	27,621	27,217
Taxes - property	5,264	4,753	4,557
Total operating expenses	191,683	185,728	190,911
Operating income	62,344	57,581	54,720
Other income (expense):	'	'	'
Interest expense	-19,725	-17,602	-16,712
AFUDC - borrowed	186	161	419
Interest income	248	376	154
AFUDC - equity	368	325	705
Other expense	-196	0	-344
Other income	367	554	145
Total other income (expense)	-18,752	-16,186	-15,633
Income from continuing operations before income taxes	43,592	41,395	39,087
Income tax expense	-13,419	-14,309	-11,990
Net income	$30,173	$27,086	$27,097

Statements_of_Comprehensive_In

Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$30,173	$27,086	$27,097
Other Comprehensive Income (Loss), Net of Tax [Abstract]	'	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax	139	-171	-70
Reclassification adjustment of benefit plan liability - net gain (loss) (net of tax of $(23), $0 and $0)	43	0	0
Reclassification adjustment of cash flow hedges settled and included in net income (loss) (net of tax of $(23), $(23) and $(23), respectively)	41	41	42
Other comprehensive income (loss), net of tax	223	-130	-28
Comprehensive income (loss), net of tax	30,396	26,956	27,069
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent, Parenthetical Disclosures [Abstract]	'	'	'
Benefit plan liability adjustments - net gain (loss), Tax	-73	93	38
Reclassification adjustment of benefit plan liability - net gain (loss) tax	-23	0	0
Reclassification adjustment of cash flow hedges settled and included in net income (loss), Tax	$23	$23	$23

Balance_Sheets

Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$2,259	$3,805
Receivables - customers, net	25,799	23,867
Receivables - affiliates	4,934	5,027
Other receivables, net	579	673
Money pool notes receivable	17,292	31,645
Materials, supplies and fuel	23,278	20,633
Deferred tax assets, net, current	2,170	16,631
Regulatory assets, current	4,891	4,998
Other current assets	4,933	5,781
Total current assets	86,135	113,060
Investments	4,431	4,359
Property, plant and equipment	1,095,884	1,024,768
Less accumulated depreciation and amortization	-334,174	-322,830
Total property, plant and equipment, net	761,710	701,938
Other assets:	'	'
Regulatory assets, non-current	40,373	48,244
Other, non-current assets	8,524	5,322
Total other assets	48,897	53,566
TOTAL ASSETS	901,173	872,923
Current liabilities:	'	'
Accounts payable	26,144	14,318
Accounts payable - affiliates	21,082	21,896
Accrued liabilities	14,966	15,477
Regulatory liabilities, current	161	37
Total current liabilities	62,353	51,728
Long-term debt	269,948	269,944
Deferred credits and other liabilities:	'	'
Deferred income tax liabilities, net, non-current	167,309	158,918
Regulatory liabilities, non-current	43,357	43,849
Benefit plan liabilities	12,105	25,888
Other, non-current liabilities	4,247	3,138
Total deferred credits and other liabilities	227,018	231,793
Stockholder's equity:	'	'
Common stock $1 par value; 50,000,000 shares authorized; 23,416,396 shares issued	23,416	23,416
Additional paid-in capital	39,575	39,575
Retained earnings	280,060	257,887
Accumulated other comprehensive loss	-1,197	-1,420
Total stockholder's equity	341,854	319,458
TOTAL LIABILITIES AND STOCKHOLDER'S EQUITY	$901,173	$872,923

Balance_Sheets_Balance_Sheet_P

Balance Sheets Balance Sheet Parantheticals (USD $)	Dec. 31, 2013	Dec. 31, 2012
Common Stock, Par Value Per Share	$1	$1
Common Stock, Shares Authorized	50,000,000	50,000,000
Common Stock, Shares, Issued	23,416,396	23,416,396
Common Stock, Shares, Outstanding	23,416,396	23,416,396

Statements_of_Cash_Flows

Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities:	'	'	'
Net income	$30,173	$27,086	$27,097
Adjustments to reconcile net income to net cash provided by operating activities -	'	'	'
Depreciation and amortization	28,125	27,621	27,217
Deferred income taxes	13,582	24,628	-2,931
AFUDC - equity	-368	-325	-705
Gain on sale of operating assets	0	0	-768
Employee benefits	3,094	3,828	2,406
Other adjustments	1,400	1,187	617
Change in operating assets and liabilities -	'	'	'
Accounts receivable and other current assets	-5,175	2,916	-973
Accounts payable and other current liabilities	1,180	-903	989
Contributions to defined benefit pension plan	-2,299	-6,835	0
Other operating activities	-3,149	-6,625	-1,515
Net cash provided by (used in) operating activities	66,563	72,578	51,434
Investing activities:	'	'	'
Property, plant and equipment additions	-74,390	-40,415	-40,910
Proceeds from sale of operating assets	0	0	1,135
Notes receivable from affiliate companies, net	6,353	-25,152	-10,615
Other investing activities	-72	469	-197
Net cash provided by (used in) investing activities	-68,109	-65,098	-50,587
Financing activities:	'	'	'
Long-term debt - repayments	0	-6,487	-80
Net cash provided by (used in) financing activities	0	-6,487	-80
Net change in cash and cash equivalents	-1,546	993	767
Cash and Cash Equivalents, at Carrying Value [Abstract]	'	'	'
Cash and cash equivalents, beginning of year	3,805	2,812	2,045
Cash and cash equivalents, end of year	$2,259	$3,805	$2,812

Statements_of_Common_Stockhold

Statements of Common Stockholder's Equity Statement (USD $)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
In Thousands, except Share data, unless otherwise specified
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2010	'	$23,416	$39,575	$247,688	($1,262)
Common Stock, Shares, Issued at Dec. 31, 2010	'	23,416,000	'	'	'
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'	'	'	'	'
Stock Issued During Period, Shares, New Issues	'	0	'	'	'
Stockholders' Equity Attributable to Parent [Abstract]	'	'	'	'	'
Stock Issued During Period, Value, New Issues	'	0	0	'	'
Net income	27,097	'	'	27,097	'
Non-cash Dividend to Parent Company	'	'	'	0	'
Other Comprehensive Income (Loss), Net of Tax	-28	'	'	'	-28
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2011	336,486	23,416	39,575	274,785	-1,290
Common Stock, Shares, Issued at Dec. 31, 2011	'	23,416,000	'	'	'
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'	'	'	'	'
Stock Issued During Period, Shares, New Issues	'	0	'	'	'
Stockholders' Equity Attributable to Parent [Abstract]	'	'	'	'	'
Stock Issued During Period, Value, New Issues	'	0	0	'	'
Net income	27,086	'	'	27,086	'
Non-cash Dividend to Parent Company	'	'	'	-43,984	'
Other Comprehensive Income (Loss), Net of Tax	-130	'	'	'	-130
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2012	319,458	23,416	39,575	257,887	-1,420
Common Stock, Shares, Issued at Dec. 31, 2012	23,416,396	23,416,000	'	'	'
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]	'	'	'	'	'
Stock Issued During Period, Shares, New Issues	'	0	'	'	'
Stockholders' Equity Attributable to Parent [Abstract]	'	'	'	'	'
Stock Issued During Period, Value, New Issues	'	0	0	'	'
Net income	30,173	'	'	30,173	'
Non-cash Dividend to Parent Company	'	'	'	-8,000	'
Other Comprehensive Income (Loss), Net of Tax	223	'	'	'	223
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2013	$341,854	$23,416	$39,575	$280,060	($1,197)
Common Stock, Shares, Issued at Dec. 31, 2013	23,416,396	23,416,000	'	'	'

Business_Description_and_Signi

Business Description and Significant Accounting Policies (Notes)	12 Months Ended
	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Business Description and Significant Accounting Policies [Text Block]	'
	BUSINESS DESCRIPTION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Business Description
	Black Hills Power, Inc. (the Company, “we,” “us” or “our”) is an electric utility serving customers in South Dakota, Wyoming and Montana. We are a wholly-owned subsidiary of BHC or the Parent, a public registrant listed on the New York Stock Exchange.
	Basis of Presentation
	The financial statements include the accounts of Black Hills Power, Inc. and also our ownership interests in the assets, liabilities and expenses of our jointly owned facilities (Note 3) and are prepared in accordance with GAAP.
	Use of Estimates and Basis of Presentation
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
	Cash Equivalents
	We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents.
	Regulatory Accounting
	Our regulated electric operations are subject to regulation by various state and federal agencies. The accounting policies followed are generally subject to the Uniform System of Accounts of FERC.
	Our regulated utility operations follow accounting standards for regulated operations and our financial statements reflect the effects of the different rate making principles followed by the various jurisdictions regulating our electric operations. If rate recovery becomes unlikely or uncertain due to competition or regulatory action, these accounting standards may no longer apply to our regulated operations. In the event we determine that we no longer meet the criteria for following accounting standards for regulated operations, the accounting impact to us could be an extraordinary non-cash charge to operations in an amount that could be material.
	Regulatory assets are included in Regulatory assets, current and Regulatory assets, non-current on the accompanying Balance Sheets. Regulatory liabilities are included in Regulatory liabilities, current and Regulatory liabilities, non-current on the accompanying Balance Sheets.
	We had the following regulatory assets and liabilities as follows as of December 31 (in thousands):
		Maximum Recovery Period (in years)	2013			2012
	Regulatory assets:
	Unamortized loss on reacquired debt(a)	14	$	2,257		$	2,501
	AFUDC(b)	45	8,327			8,460
	Employee benefit plans(c)	13	15,233			27,001
	Deferred energy costs(a)	1	7,711			6,892
	Flow through accounting(a)	35	9,723			8,019
	Other regulatory assets(a)	2	2,013			369
	Total regulatory assets		$	45,264		$	53,242
	Regulatory liabilities:
	Cost of removal for utility plant(a)	53	$	30,467		$	26,630
	Employee benefit plans(d)	13	10,177			15,689
	Other regulatory liabilities(e)	13	2,874			1,567
	Total regulatory liabilities		$	43,518		$	43,886
	____________________
	(a)    Recovery of costs but not allowed a rate of return.
	(b)	In addition to recovery of costs, we are allowed a rate of return.
	(c)	In addition to recovery of costs, we are allowed a return on approximately $24 million according to the approved rate case.
	(d)	Approximately $13 million is included in our rate base calculation as a reduction to rate base.
	(e)	Approximately $0.8 million is included in our rate base calculation as a reduction to rate base.
	Regulatory assets represent items we expect to recover from customers through probable future rates.
	Unamortized Loss on Reacquired Debt - The early redemption premium on reacquired bonds is being amortized over the remaining term of the original bonds.
	AFUDC - The equity component of AFUDC is considered a permanent difference for tax purposes with the tax benefit being flowed through to customers as prescribed or allowed by regulators. If, based on a regulator’s action, it is probable the utility will recover the future increase in taxes payable represented by this flow-through treatment through a rate revenue increase, a regulatory asset is recognized. This regulatory asset itself is a temporary difference for which a deferred tax liability must be recognized. Accounting standards for income taxes specifically address AFUDC-equity, and require a gross-up of such amounts to reflect the revenue requirement associated with a rate-regulated environment.
	Employee Benefit Plans - Employee benefit plans include the unrecognized prior service costs and net actuarial loss associated with our defined benefit pension plans and post-retirement benefit plans in regulatory assets rather than in accumulated other comprehensive income.
	Deferred Energy Costs - Deferred energy and fuel cost adjustments represent the cost of electricity delivered to our utility customers that are either higher or lower than the current rates and will be recovered or refunded in future rates. Deferred energy and fuel cost adjustments are recorded and recovered or amortized as approved by the appropriate state commission.
	Flow-Through Accounting - Under flow-through accounting, the income tax effects of certain tax items are reflected in our cost of service for the customer in the year in which the tax benefits are realized and result in lower utility rates. This regulatory treatment was applied to the tax benefit generated by repair costs that were previously capitalized for tax purposes in a rate case settlement that was reached in 2010. In this instance, the agreed upon rate increase was less than it would have been absent the flow-through treatment. A regulatory asset established to reflect the future increases in income taxes payable will be recovered from customers as the temporary differences reverse.
	Regulatory liabilities represent items we expect to refund to customers through probable future decreases in rates.
	Cost of Removal for Utility Plant - Cost of removal for utility plant represents the estimated cumulative net provisions for future removal costs included in depreciation expense for which there is no legal obligation for removal.
	Employee Benefit Plans - Employee benefit plans represent the cumulative excess of pension and retiree healthcare costs recovered in rates over pension expense recorded in accordance with accounting standards for compensation - retirement benefits. In addition, this regulatory liability includes the income tax effect of the adjustment required under accounting for compensation - defined benefit plans, to record the full pension and post-retirement benefit obligations. Such income tax effect has been grossed-up to account for the revenue requirement aspect of a rate regulated environment.
	Accounts Receivable and Allowance for Doubtful Accounts
	Accounts receivable consist of sales to residential, commercial, industrial, municipal and other customers all of which do not bear interest. These accounts receivable are stated at billed and unbilled amounts net of write-offs or payment received.
	We maintain an allowance for doubtful accounts which reflects our best estimate of uncollectible trade receivables. We regularly review our trade receivable allowances by considering such factors as historical experience, credit worthiness, the age of the receivable balances and current economic conditions that may affect collectibility. The allowance is calculated by applying estimated write-off factors to various classes of outstanding receivables, including unbilled revenue. The write-off factors used to estimate uncollectible accounts are based upon consideration of both historical collections experience and management’s best estimate of future collection success given the existing collections environment.
	Following is a summary of accounts receivable at December 31 (in thousands):
		2013			2012
	Accounts receivable trade	$	16,300		$	14,965
	Unbilled revenues	9,719			9,004
	Allowance for doubtful accounts	(220		)	(102		)
	Net accounts receivable	$	25,799		$	23,867
	Revenue Recognition
	Revenue is recognized when there is persuasive evidence of an arrangement with a fixed or determinable price, delivery has occurred or services have been rendered, and collectibility is reasonably assured. Taxes collected from our customers are recorded on a net basis (excluded from Revenue).
	Utility revenues are based on authorized rates approved by the state regulatory agencies and the FERC. Revenues related to the sale, transmission and distribution of energy, and delivery of service are generally recorded when service is rendered or energy is delivered to customers. To the extent that deliveries have occurred but a bill has not been issued, we accrue an estimate of the revenue since the latest billing. This estimate is calculated based upon several factors including billings through the last billing cycle in a month, and prices in effect in our jurisdictions. Each month the estimated unbilled revenue amounts are trued-up and recorded in Receivables- customers, net on the accompanying Balance Sheets.
	Materials, Supplies and Fuel
	Materials, supplies and fuel used for construction, operation and maintenance purposes are generally stated on a weighted-average cost basis.
	Deferred Financing Costs
	Deferred financing costs are amortized using the effective interest method over the term of the related debt.
	Property, Plant and Equipment
	Additions to property, plant and equipment are recorded at cost when placed in service. Included in the cost of regulated construction projects is AFUDC, which represents the approximate composite cost of borrowed funds and a return on equity used to finance a regulated utility project. The cost of regulated electric property, plant and equipment retired, or otherwise disposed of in the ordinary course of business, less salvage, is charged to accumulated depreciation. Removal costs associated with non-legal obligations are reclassified from accumulated depreciation and reflected as regulatory liabilities. Ordinary repairs and maintenance of property, except as allowed under rate regulations, are charged to operations as incurred.
	Depreciation provisions for regulated electric property, plant and equipment are computed on a straight-line basis using an annual composite rate of 2.1% in 2013, 2.2% in 2012 and 2.2% in 2011.
	Derivatives and Hedging Activities
From time to time we utilize risk management contracts including forward purchases and sales to hedge the price of fuel for our combustion turbines and fixed-for-float swaps to fix the interest on any variable rate debt. Contracts that qualify as derivatives under accounting standards for derivatives, and that are not exempted such as normal purchase/normal sale, are required to be recorded in the balance sheet as either an asset or liability, measured at its fair value. Accounting standards for derivatives require that changes in the derivative instrument’s fair value be recognized currently in earnings unless specific hedge accounting criteria are met.
Accounting standards for derivatives allow hedge accounting for qualifying fair value and cash flow hedges. Gain or loss on a derivative instrument designated and qualifying as a fair value hedging instrument as well as the offsetting loss or gain on the hedged item attributable to the hedged risk should be recognized currently in earnings in the same accounting period. Conversely, the effective portion of the gain or loss on a derivative instrument designated and qualifying as a cash flow hedging instrument should be reported as a component of other comprehensive income and be reclassified into earnings or as a regulatory asset or regulatory liability, net of tax, in the same period or periods during which the hedged forecasted transaction affects earnings. The remaining gain or loss on the derivative instrument, if any, is recognized currently in earnings.
Fair Value Measurements
Accounting standards for fair value measurements provide a single definition of fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date and also requires disclosures and establishes a fair value hierarchy that prioritizes the inputs used to measure fair value. The fair value hierarchy ranks the quality and reliability of the information used to determine fair values giving the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements).
Financial assets and liabilities carried at fair value are classified and disclosed in one of the following three categories:
Level 1 - Unadjusted quoted prices available in active markets that are accessible at the measurement date for identical unrestricted assets or liabilities.
Level 2 - Pricing inputs include quoted prices for identical or similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and inputs that are derived principally from or corroborated by observable market data by correlation or other means.
Level 3 - Pricing inputs include significant inputs that are generally less observable from objective sources.
Impairment of Long-Lived Assets
We periodically evaluate whether events and circumstances have occurred which may affect the estimated useful life or the recoverability of the remaining balance of our long-lived assets. If such events or circumstances were to indicate that the carrying amount of these assets was not recoverable, we would estimate the future cash flows expected to result from the use of the assets and their eventual disposition. If the sum of the expected future cash flows (undiscounted and without interest charges) was less than the carrying amount of the long-lived assets, we would recognize an impairment loss.
Income Taxes
We file a federal income tax return with other members of the Parent’s consolidated group. For financial statement purposes, federal income taxes are allocated to the individual companies based on amounts calculated on a separate return basis.
We use the liability method in accounting for income taxes. Under the liability method, deferred income taxes are recognized at currently enacted income tax rates, to reflect the tax effect of temporary differences between the financial and tax basis of assets and liabilities, as well as operating loss and tax credit carryforwards. Such temporary differences are the result of provisions in the income tax law that either require or permit certain items to be reported on the income tax return in a different period than they are reported in the financial statements. We classify deferred tax assets and liabilities into current and non-current amounts based on the classification of the related assets and liabilities.
It is the Parent’s policy to apply the flow-through method of accounting for investment tax credits. Under the flow-through method, investment tax credits are reflected in net income as a reduction to income tax expense in the year they qualify. Another acceptable accounting method and an exception to this general policy is to apply the deferral method whereby the credit is amortized as a reduction of income tax expense over the useful lives of the related property which gave rise to the credits.
We recognize interest income or interest expense and penalties related to income tax matters in Income tax (expense) benefit on the Statements of Income. We account for uncertainty in income taxes recognized in the financial statements in accordance with accounting standards for income taxes. The unrecognized tax benefit is classified in Other - non-current liabilities on the accompanying Balance Sheets. See Note 6 for additional information.
Recently Adopted Accounting Standards
Other Comprehensive Income: Presentation of Comprehensive Income, ASU 2011-05 and Deferral of the Effective Date for Amendments to the Presentation of Reclassification of Items Out of Accumulated Other Comprehensive Income in Accounting Standards Update 2011-05 and ASU 2011-12
FASB issued an accounting standards update amending ASC 220 to improve the comparability, consistency and transparency of reporting of comprehensive income. It amends existing guidance by allowing only two options for presenting the components of net income and other comprehensive income: (1) in a single continuous financial statement, statement of comprehensive income or (2) in two separate but consecutive financial statements, consisting of an income statement followed by a separate statement of other comprehensive income. Also, items that are reclassified from other comprehensive income to net income must be presented on the face of the financial statements. ASU No. 2011-05 requires retrospective application, and it is effective for fiscal years, and interim periods within those years, beginning after December 15, 2011, with early adoption permitted. In December 2011, FASB issued ASU 2011-12. ASU 2011-12 indefinitely deferred the provisions of ASU 2011-05 requiring the presentation of reclassification adjustments for items reclassified from other comprehensive income to net income be presented on the face of the financial statements. Ultimately FASB chose not to reinstate the reclassification adjustment requirements in ASU 2011-05 but instead issued ASU 2013-02 in February 2013. The adoption of this standard did not have an impact on our financial position, results of operations or cash flows.
Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income, ASU 2013-02
In February 2013, the FASB issued new disclosure requirements for items reclassified out of AOCI to expand the disclosure requirements in ASC 220, Comprehensive Income, for presentation of changes in AOCI. ASU 2013-02 requires disclosure of (1) changes in components of other comprehensive income, (2) for items reclassified out of AOCI and into net income in their entirety, the effect of the reclassification on each affected net income line item and (3) cross references to other disclosures that provide additional detail for components of other comprehensive income that are not reclassified in their entirety to net income. Disclosures are required either on the face of the statements of income or as a separate disclosure in the notes to the financial statements. The new disclosure requirements are effective for interim and annual periods beginning after December 15, 2012. The adoption of this standard did not have an impact on our financial position, results of operations or cash flows.
Recently Issued Accounting Pronouncements and Legislation
Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists
In July 2013, the FASB issued an amendment to accounting for income taxes which provides guidance on financial statement presentation of an unrecognized tax benefit when an NOL carryforward, a similar tax loss, or a tax credit carryforward exists. The objective in issuing this amendment is to eliminate diversity in practice resulting from a lack of guidance on this topic in current GAAP. Under the amendment, an entity must present an unrecognized tax benefit, or a portion of an unrecognized tax benefit, in the financial statements as a reduction to a deferred tax asset for an NOL carryforward, a similar tax loss, or a tax credit carryforward except under certain conditions. The amendment is effective for fiscal years beginning after December 15, 2013, and interim periods within those years and should be applied to all unrecognized tax benefits that exist as of the effective date. The adoption of this standard is not expected to have an impact on our financial position, results of operations or cash flows.
Final Tangible Personal Property Regulations, IRS Treasury Decision 9636
In September 2013, the U.S. Treasury issued final regulations addressing the tax consequences associated with amounts paid to acquire, produce, or improve tangible property. The regulations have the effect of a change in law and as a result the impact should be taken into account in the period of adoption. In general, such regulations apply to tax years beginning on or after January 1, 2014, with early adoption permitted. We expect that implementation of most, if not all, of the provisions of the final regulations to occur in 2014. Procedural guidance is expected from IRS in early 2014 to facilitate implementation. Analysis performed to date indicates no material impact to our financial statements.

Property_Plant_and_Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment Disclosure [Text Block]	'
	PROPERTY, PLANT AND EQUIPMENT
	Property, plant and equipment at December 31 consisted of the following (dollars in thousands):
					2013				2012
					Weighted				Weighted
					Average				Average	Lives (in years)
		2013			Useful Life (in years)	2012			Useful Life (in years)	Minimum	Maximum
	Electric plant:
	Production	$	512,444		51	$	510,674		51	45	65
	Transmission	115,149			46	115,092			46	40	60
	Distribution	315,971			39	304,113			38	16	45
	Plant acquisition adjustment (a)	4,870			32	4,870			32	32	32
	General	70,228			22	71,802			22	8	45
	Total plant-in-service	1,018,662				1,006,551
	Construction work in progress	77,222				18,217
	Total electric plant	1,095,884				1,024,768
	Less accumulated depreciation and amortization	(334,174		)		(322,830		)
	Electric plant net of accumulated depreciation and amortization	$	761,710			$	701,938
	__________________
	(a)	The plant acquisition adjustment is included in rate base and is being recovered with 17 years remaining.

Jointly_Owned_Facilities

Jointly Owned Facilities	12 Months Ended
	Dec. 31, 2013
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]	'
Jointly Owned Facilities [Text Block]	'
	JOINTLY OWNED FACILITIES
	We use the proportionate consolidation method to account for our percentage interest in the assets, liabilities and expenses of the following facilities:
	•	We own a 20% interest in the Wyodak Plant (the “Plant”), a coal-fired electric generating station located in Campbell County, Wyoming. PacifiCorp owns the remaining ownership percentage and is the operator of the Plant. We receive our proportionate share of the Plant’s capacity and are committed to pay our share of its additions, replacements and operating and maintenance expenses.
	•	We own a 35% interest in, and are the operator of, the Converter Station Site and South Rapid City Interconnection (the transmission tie), an AC-DC-AC transmission tie. Basin Electric owns the remaining ownership percentage. The transmission tie provides an interconnection between the Western and Eastern transmission grids, which provides us with access to both the WECC region and the MAPP region. The total transfer capacity of the transmission tie is 400 MW - 200 MW West to East and 200 MW from East to West. We are committed to pay our proportionate share of the additions, replacements and operating and maintenance expenses.
	•	We own a 52% interest in the Wygen III power plant. MDU and the City of Gillette each owns an undivided ownership interest in Wygen III and are obligated to make payments for costs associated with administrative services and a proportionate share of the costs of operating the plant for the life of the facility. We retain responsibility for plant operations.
	The investments in our jointly owned plants and accumulated depreciation are included in the corresponding captions in the accompanying Balance Sheets. Our share of direct expenses of the Plant is included in the corresponding categories of operating expenses in the accompanying Statements of Income. Each of the respective owners is responsible for providing its own financing.
	As of December 31, 2013, our interests in jointly-owned generating facilities and transmission systems included on our Balance Sheets were as follows (in thousands):
	Interest in jointly-owned facilities	Plant in Service		Construction Work in Progress		Accumulated Depreciation
	Wyodak Plant	$	109,800	$	192	$	50,595
	Transmission Tie	$	19,648	$	—	$	4,741
	Wygen III	$	131,468	$	713	$	10,593

Long_term_Debt

Long term Debt	12 Months Ended
	Dec. 31, 2013
Long-term Debt, Unclassified [Abstract]	'
Long term Debt [Text Block]	'
	LONG-TERM DEBT
	Long-term debt outstanding at December 31 was as follows (in thousands):
		Maturity Date	Interest Rate		2013			2012
	First Mortgage Bonds due 2032	August 15, 2032	7.23	%	$	75,000		$	75,000
	First Mortgage Bonds due 2039	November 1, 2039	6.125	%	180,000			180,000
	Unamortized discount, First Mortgage Bonds due 2039				(107		)	(111		)
	Pollution control revenue bonds due 2024	October 1, 2024	5.35	%	12,200			12,200
	Series 94A Debt(a)	June 1, 2024	0.75	%	2,855			2,855
	Long-term debt				$	269,948		$	269,944
	___________________
	(a)	Variable interest rate at December 31, 2013.
	Net deferred financing costs of approximately $2.8 million and $2.9 million were recorded on the accompanying Balance Sheets in Other, non-current assets at December 31, 2013 and 2012, respectively, and are being amortized over the term of the debt. Amortization of deferred financing costs of approximately $0.1 million, $0.2 million and $0.5 million for the years ended December 31, 2013, 2012 and 2011, respectively, are included in Interest expense on the accompanying Statements of Income.
	Substantially all of our property is subject to the lien of the indenture securing our first mortgage bonds. First mortgage bonds may be issued in amounts limited by property, earnings and other provisions of the mortgage indentures. We were in compliance with our debt covenants at December 31, 2013.
	Long-term Debt Maturities
	Scheduled maturities of our outstanding long-term debt (excluding unamortized discounts) are as follows (in thousands):
	2014	$	—
	2015	$	—
	2016	$	—
	2017	$	—
	2018	$	—
	Thereafter	$	270,055

Fair_Value_Instruments

Fair Value Instruments	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value of Financial Instruments	'
	FAIR VALUE OF FINANCIAL INSTRUMENTS
	The estimated fair values of our financial instruments at December 31 were as follows (in thousands):
		2013				2012
		Carrying Value		Fair Value		Carrying Value		Fair Value
	Cash and cash equivalents (a)	$	2,259	$	2,259	$	3,805	$	3,805
	Long-term debt, including current maturities (b)	$	269,948	$	317,531	$	269,944	$	359,567
	_______________
	(a)	Fair value approximates carrying value due to either short-term length of maturity or variable interest rates that approximate prevailing market rates and therefore is classified in Level 1 in the fair value hierarchy.
	(b)	Long-term debt is valued using the market approach based on observable inputs of quoted market prices and yields available for debt instruments either directly or indirectly for similar maturities and debt ratings in active markets and therefore is classified in Level 2 in the fair value hierarchy. The carrying amount of our variable rate debt approximates fair value due to the variable interest rates with short reset periods. For additional information on our long-term debt, see Note 4 to the Financial Statements.
	The following methods and assumptions were used to estimate the fair value of each class of our financial instruments.
	Cash and Cash Equivalents
	Included in cash and cash equivalents is cash and overnight repurchase agreement accounts. As part of our cash management process, excess operating cash is invested in overnight repurchase agreements with our bank. Repurchase agreements are not deposits and are not insured by the U.S. Government, the FDIC or any other government agency and involve investment risk including possible loss of principal. We believe however, that the market risk arising from holding these financial instruments is minimal.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Income Tax Disclosure [Text Block]	'
	INCOME TAXES
	Income tax expense (benefit) from continuing operations for the years ended December 31 were as follows (in thousands):
		2013			2012			2011
	Current	$	(163	)	$	(10,319	)	$	14,921
	Deferred	13,582			24,628			(2,931		)
	Total income tax expense	$	13,419		$	14,309		$	11,990
	The temporary differences which gave rise to the net deferred tax liability, for the years ended December 31 were as follows (in thousands):
		2013			2012
	Deferred tax assets:
	Employee benefits	$	4,567		$	5,094
	Net operating loss	4,197			10,441
	Regulatory liabilities	6,398			13,433
	Other	2,193			2,381
	Total deferred tax assets	17,355			31,349
	Deferred tax liabilities:
	Accelerated depreciation and other plant related differences	(161,990		)	(154,989		)
	AFUDC	(8,190		)	(5,499		)
	Regulatory assets	(3,540		)	(5,767		)
	Employee benefits	(3,467		)	(3,610		)
	Deferred costs	(4,240		)	(2,608		)
	Other	(1,067		)	(1,163		)
	Total deferred tax liabilities	(182,494		)	(173,636		)
	Net deferred tax assets (liabilities)	$	(165,139	)	$	(142,287	)
	The effective tax rate differs from the federal statutory rate for the years ended December 31, as follows:
		2013		2012		2011
	Federal statutory rate	35	%	35	%	35	%
	Amortization of excess deferred and investment tax credits	(0.3	)	(0.3	)	(0.4	)
	Equity AFUDC	—		(0.1	)	(0.6	)
	Flow through adjustments *	(2.5	)	(3.5	)	(3.4	)
	Prior year deferred adjustment **	—		3.6		—
	Tax credits	(0.8	)	—		—
	Other	(0.6	)	(0.1	)	0.1
		30.8	%	34.6	%	30.7	%
	_________________________
	*	The flow-through adjustments relate primarily to an accounting method change for tax purposes that allows us to take a current tax deduction for repair costs that continue to be capitalized for book purposes. We recorded a deferred income tax liability in recognition of the temporary difference created between book and tax treatment and we flowed the tax benefit through to our customers in the form of lower rates as a result of a rate case settlement that occurred during 2010. A regulatory asset was established to reflect the recovery of future increases in taxes payable from customers as the temporary differences reverse. As a result of this regulatory treatment, we continue to record a tax benefit consistent with the flow through method.
	**	The adjustment was a non-recurring unfavorable true-up attributable to property related deferred income taxes. The removal of the impact of such an adjustment is more appropriately reflective of the effective rate on a recurring basis.
	The following table reconciles the total amounts of unrecognized tax benefits, without interest, included in Other deferred credits and other liabilities on the accompanying Balance Sheet (in thousands):
		2013			2012
	Unrecognized tax benefits at January 1	$	2,078		$	3,595
	Reductions for prior year tax positions	(155		)	(1,586		)
	Additions for current year tax positions	520			69
	Unrecognized tax benefits at December 31	$	2,443		$	2,078
	The reductions for prior year tax positions relate to the reversal through otherwise allowed tax depreciation. The total amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate is approximately $0.5 million.
	It is our continuing practice to recognize interest and/or penalties related to income tax matters in income tax expense. During the years ended December 31, 2013 and 2012, the interest expense recognized was not material to our financial results.
	We file income tax returns in the United States federal jurisdictions as a member of the BHC consolidated group. We do not anticipate that total unrecognized tax benefits will significantly change due to settlement of any audits or the expiration of statutes of limitations prior to December 31, 2014.
	At December 31, 2013, we have federal NOL carry forward of $14 million, expiring in 2031. Ultimate usage of this NOL depends upon our ability to generate future taxable income, which is expected to occur within the prescribed carryforward period.

Comprehensive_Income_Comprehen

Comprehensive Income Comprehensive Income (Loss) (Note Block)	12 Months Ended
	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Comprehensive Income (Loss) Note [Text Block]	'
	COMPREHENSIVE INCOME
	The components of the reclassification adjustments for the period, net of tax, included in Other Comprehensive Income were as follows (in thousands):
		Derivatives Designated as Cash Flow Hedges	Amounts Reclassified from AOCI
			2013			2012
	Gains and Losses on cash flow hedges
	Interest rate swaps	Interest expense	$	64		$	64
	Income tax	Income tax benefit (expense)	(23		)	(23		)
	Total reclassification adjustments related to cash flow hedges, net of tax		$	41		$	41
	Amortization of defined benefit plans:
	Actuarial gain (loss)	Operations and maintenance	$	66		$	—
	Income tax	Income tax benefit (expense)	(23		)	—
	Total reclassification adjustments related to defined benefit plans, net of tax		$	43		$	—
	Derivatives designated as cash flow hedges relate to a treasury lock entered into in August 2002 to hedge $50 million of our First Mortgage Bonds due on August 15, 2032. The treasury lock cash settled on August 8, 2002, the bond pricing date, and resulted in a $1.8 million loss. The treasury lock is treated as a cash flow hedge and the resulting loss is carried in Accumulated Other Comprehensive Loss and is being amortized over the life of the related bonds.
	Balances by classification included within Accumulated other comprehensive loss on the accompanying Balance Sheets were as follows (in thousands):
		Derivatives Designated as Cash Flow Hedges
		Interest Rate Swaps			Employee Benefit Plans			Total
	As of December 31, 2012	$	(760	)	$	(660	)	$	(1,420	)
	Other comprehensive income (loss)	41			182			223
	As of December 31, 2013	$	(719	)	$	(478	)	$	(1,197	)
		Derivatives Designated as Cash Flow Hedges
		Interest Rate Swaps			Employee Benefit Plans			Total
	As of December 31, 2011	$	(801	)	$	(489	)	$	(1,290	)
	Other comprehensive income (loss)	41			(171		)	(130		)
	As of December 31, 2012	$	(760	)	$	(660	)	$	(1,420	)

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Pension and Other Postretirement Benefits Disclosure [Text Block]	'
	EMPLOYEE BENEFIT PLANS
	Funded Status of Benefit Plans
	The funded status of the postretirement benefit plan is required to be recognized in the statement of financial position. The funded status for the pension plan is measured as the difference between the projected benefit obligation and the fair value of plan assets. The funded status for all other benefit plans is measured as the difference between the accumulated benefit obligation and the fair value of plan assets. A liability is recorded for an amount by which the benefit obligation exceeds the fair value of plan assets or an asset is recorded for any amount by which the fair value of plan assets exceeds the benefit obligation. The measurement date of the plans is December 31, our year-end balance sheet date. As of December 31, 2013, the unfunded status of our Defined Benefit Pension Plan was $3.8 million, the unfunded status of our Supplemental Non-qualified Defined Benefit Plans was $3.1 million and the unfunded status of our Non-pension Defined Benefit Postretirement Healthcare Plans was $5.9 million.
	We apply accounting standards for regulated operations, and accordingly, the unrecognized net periodic benefit cost that would have been reclassified to Accumulated other comprehensive income (loss) was alternatively recorded as a regulatory asset or regulatory liability, net of tax.
	Defined Benefit Pension Plan
	We have a noncontributory defined benefit pension plan (“Pension Plan”) covering employees who meet certain eligibility requirements. The benefits are based on years of service and compensation levels during the highest five consecutive years of the last ten years of service. Our funding policy is in accordance with the federal government’s funding requirements. The Pension Plan’s assets are held in trust and consist primarily of equity and fixed income investments.
	The Pension Plan has been frozen to new employees and certain employees who did not meet age and service based criteria at the time the Plan was frozen. Plan benefits are based on years of service and calculations of average earnings during a specific time period prior to retirement.
	As of December 31, 2012, certain Plan investments were transferred to a Master Trust that was established for the investment of assets of the Plan and other Employer-sponsored retirement plans. Each participating retirement plan has an undivided interest in the Master Trust.
	On October 29, 2012, the Board of Directors approved a new Investment Policy. The objective of the Investment Policy is to manage assets in such a way that will allow the eventual settlement of our obligations to the Plans’ beneficiaries. To meet this objective, our pension plan assets are managed by an outside adviser using a portfolio strategy that will provide liquidity to meet the Plans’ benefit payment obligations and an asset allocation that will comprise a mix of return-seeking and liability-hedging assets. Our Pension Plan funding policy is in accordance with the federal government’s funding requirements. The Pension Plan’s assets are held in trust and consist primarily of equity, fixed income and hedged investments. The expected long-term rate of return for investments was 7.25% and 7.25% for the 2013 and 2012 plan years, respectively.
	Pension Plan Assets
	The percentages of total plan asset fair value by investment category of our Pension Plan assets at December 31 were as follows:
		2013		2012
	Equity securities	26	%	51	%
	Real estate	4	%	—	%
	Fixed income funds	58	%	48	%
	Cash and cash equivalents	1	%	1	%
	Hedge funds	11	%	—	%
	Total	100	%	100	%
	Supplemental Non-qualified Defined Benefit Retirement Plans
	We have various supplemental retirement plans (“Supplemental Plans”) for key executives. The Supplemental Plans are non-qualified defined benefit plans. The Supplemental Plans are subject to various vesting schedules.
	Supplemental Plan Assets
	We do not fund our Supplemental Plans. We fund on a cash basis as benefits are paid.
	Non-pension Defined Benefit Postretirement Healthcare Plan
	Employees who are participants in our Non-Pension Postretirement Healthcare Plan (“Healthcare Plan”) and who retire on or after attaining minimum age and years of service requirements are entitled to postretirement healthcare benefits. These benefits are subject to premiums, deductibles, co-payment provisions and other limitations. We may amend or change the Healthcare Plan periodically. We are not pre-funding our retiree medical plan. We have determined that the Healthcare Plan’s post-65 retiree prescription drug plans are actuarially equivalent and qualify for the Medicare Part D subsidy.
	Plan Assets
	We do not fund our Healthcare Plans. We fund on a cash basis as benefits are paid.
	Plan Contributions and Estimated Cash Flows
	Contributions made to the Pension Plans are cash contributions made directly to the Pension Plan Trust accounts. Healthcare and Supplemental Plan contributions are made in the form of benefit payments. Contributions for the years ended December 31 were as follows (in thousands):
		2013			2012
	Defined Benefit Plans
	Defined Benefit Pension Plan	$	2,299		$	6,835
	Non-pension Defined Benefit Postretirement Healthcare Plan	$	578		$	835
	Supplemental Non-qualified Defined Benefit Plan	$	217		$	256
	Defined Contribution Plans
	Company Retirement Contribution	$	421		$	404
	Matching Contributions	$	1,301		$	1,328
	We do not intend to make a contribution to our employee defined benefit pension plan in 2014.
	Fair Value Measurements
	As required by accounting standards for fair value measurements, assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect their placement within the fair value hierarchy levels. The following tables set forth, by level within the fair value hierarchy, the assets that were accounted for at fair value on a recurring basis as of December 31 (in thousands):
	Defined Benefit Pension Plan	2013
		Level 1			Level 2			Level 3			Total Fair Value
	AXA Equitable General Fixed Income	$	—		$	213		$	—		$	213
	Common Collective Trust - Cash and Cash Equivalents	—			252			—			252
	Common collective trust - equity	—			14,833			—			14,833
	Common collective trust - fixed income	—			32,742			—			32,742
	Common collective trust - real estate	—			682			1,718			2,400
	Hedge funds	—			—			5,965			5,965
	Total investments measured at fair value	$	—		$	48,722		$	7,683		$	56,405
	Defined Benefit Pension Plan	2012
		Level 1			Level 2			Level 3			Total Fair Value
	Cash and cash equivalents	$	535		$	—		$	—		$	535
	Common collective trust - equity	—			27,267			—			27,267
	Common collective trust - fixed income	—			21,127			—			21,127
	Structured products	—			4,536			—			4,536
	Total investments measured at fair value	$	535		$	52,930		$	—		$	53,465
	Cash and Cash Equivalents: This category is comprised of the AXA Equitable General Fixed Income Fund wand Common Collective Trusts - cash and cash equivalents. The AXA Equitable General Fixed Income Fund is a fund of diversified portfolios, primarily composed of fixed income instruments. Assets are invested in long-term holdings, such as commercial, agricultural and residential mortgages, publicly traded and privately place bonds and real estate as well as short-term bonds. Fair values of mortgage loans are measured by discounting future contractual cash flows to be received on the mortgage loans using interest rates at which loans with similar characteristics. The discount rate is derived from taking the appropriate U.S. Treasury rate with a like term. The fair value of public fixed maturity securities are generally based on prices obtained from independent valuation service provides with reasonableness prices compared with directly observable market trades. The fair value of privately placed securities are determined using a discounted cash flow model. These models use observable inputs with a discount rate based upon the average of spread surveys collected from private market intermediaries and industry sector of the issuer.
	Common Collective Trust: The Pension Plan owns units of the Common Collective Trust funds that they are utilizing in their portfolio. The value of each unit of any fund as of any valuation date shall be determined by calculating the total value of such fund’s assets as of the close of business on such valuation date, deducting its total liabilities as of such time and date, and then dividing the so-determined net asset value of such fund by the total number of units of such fund outstanding on the date of valuation.
	Common Collective Trust-Real Estate Fund: This fund is valued based on various factors of the underlying real estate properties, including market rent, market rent growth, occupancy levels, etc. As part of the trustee’s valuation process, properties are externally appraised generally on an annual basis. The appraisals are conducted by reputable independent appraisal firms and signed by appraisers that are members of the Appraisal Institute, with professional designation of Member, Appraisal Institute. All external appraisals are performed in accordance with the Uniform Standards of Professional Appraisal Practices. We receive monthly statements from the trustee, along with the annual schedule of investments, and rely on these reports for pricing the units of the fund. Certain of the funds’ assets contain participant withdrawal policy and, therefore, are categorized as Level 3. The funds without participant withdrawal limitations are categorized as Level 2.
	Hedge Funds: Hedge funds represent investments in other investment funds that seek a return utilizing a number of diverse investment strategies. The strategies, when combined aim to reduce volatility and risk while attempting to deliver positive returns under all market conditions. Amounts are reported on a one-month lag. The fair value of hedge funds is determined using net asset value per share based on the fair value of the hedge fund’s underlying investments. Generally, shares may be redeemed at the end of each quarter, after a lockup period of one-year, with a 65 day notice and is limited to a percentage of total net asset value of the fund. The net asset values are based on the fair value of each fund’s underlying investments. There are no unfunded commitments related to these hedge funds.
	Structured Products: Investments are created through the process of financial engineering (that is, by combining underlying securities like equity, bonds, or indices with derivatives). The value of derivative securities, such as options, forwards and swaps is determined by (respectively, derives from) the prices of the underlying securities.
	The following table sets forth a summary of changes in the fair value of the Defined Benefit Pension Plans’ Level 3 assets for the period ended December 31 (in thousands):
		2013
	Balance, beginning of period	$	—
Transfers	1,550
Purchase	5,834
Unrealized gain (loss)	317
Realized gain (loss)	(3		)
Settlements	(15		)
Balance, end of period	$	7,683
The following table presents the quantitative information about Level 3 fair value measurements (dollars in thousands):
	Fair Value at			Valuation	Level 3	Range (Weighted)
	31-Dec-13			Technique	Input	Average
Assets:
Common Collective Trust - Real Estate (a)	$	1,718		Market Approach	Redemption Restriction	N/A
Hedge Funds (b)	$	5,965		Market Approach	Redemption Restriction	N/A
_____________
(a)	The underlying net asset value in the Common Collective Trust - Real Estate fund is determined by appraisal of the properties held in the Trust. As part of the Trustee's valuation process, properties are externally appraised generally on an annual basis. The appraisals are conducted by reputable independent appraisal firms and signed by appraisers that are members of the Appraisal Institute, with the professional designation of Member, Appraisal Institute. All external appraisals are performed in accordance with the Uniform Standards of Professional Appraisal Practices. We receive monthly statements from the Trustee along with the annual schedule of investments and rely on these reports for pricing the units of the fund. The fund does contain a participant withdrawal policy.
(b)	The fair value of Level 3 is determined based on pricing provided or reviewed by third-party administrator to our investment managers. While the input amounts used by the pricing vendor in determining fair value are not provided, and therefore, unavailable for our review, the asset results are reviewed and monitored to ensure the fair values are reasonable and in line with market experience in similar asset classes. Additionally, the audited financial statements of the funds will be reviewed at the time they are issued.
Plan Reconciliations
The following tables provide a reconciliation of the Employee Benefit Plan’s obligations and fair value of assets, components of the net periodic expense and elements of regulatory assets and liabilities and AOCI (in thousands):
Benefit Obligations
	Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
	2013			2012			2013			2012			2013			2012
Change in benefit obligation:
Projected benefit obligation at beginning of year	$	69,820		$	65,557		$	3,427		$	2,292		$	6,766		$	8,207
Service cost	852			765			—			—			216			214
Interest cost	2,969			2,969			133			104			239			343
Actuarial loss (gain)	(7,818		)	4,510			(212		)	1,287			(459		)	(1,748		)
Amendments (a)	—			—			—			—			(342		)	—
Benefits paid	(4,850		)	(2,850		)	(217		)	(256		)	(1,045		)	(835		)
Asset transfer (to) from affiliate	(750		)	(1,131		)	—			—			(75		)	26
Plan curtailment reduction	—			—			—			—			—			—
Medicare Part D adjustment	—			—			—			—			82			71
Plan participants’ contributions	—			—			—			—			468			488
Projected benefit obligation at end of year	$	60,223		$	69,820		$	3,131		$	3,427		$	5,850		$	6,766
_______________
(a)	Reflects Board of Directors approval of increase to Company’s contribution to RMSA account.
A reconciliation of the fair value of Plan assets (as of the December 31 measurement date) is as follows (in thousands):
	Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
	2013			2012			2013			2012			2013			2012
Beginning market value of plan assets	$	53,465		$	45,017		$	—		$	—		$	—		$	—
Investment income	6,070			5,240			—			—			—			—
Benefits paid	(4,850		)	(2,850		)	—			—			—			—
Employer contributions	2,299			6,835			—			—			—			—
Asset transfer to affiliate	(579		)	(777		)	—			—			—			—
Ending market value of plan assets	$	56,405		$	53,465		$	—		$	—		$	—		$	—
Amounts recognized in the Balance Sheets at December 31 consist of (in thousands):
	Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Plan
	2013			2012			2013			2012			2013			2012
Regulatory asset (liability)	$	13,735		$	26,683		$	—		$	—		$	2,781		$	(2,174	)
Current (liability)	$	—		$	—		$	(216	)	$	(216	)	$	(491	)	$	(438	)
Non-current (liability)	$	(3,818	)	$	(16,356	)	$	(2,915	)	$	(3,211	)	$	(5,372	)	$	(6,321	)
Accumulated Benefit Obligation (dollars in thousands)
	Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
	2013			2012			2013			2012			2013			2012
Accumulated benefit obligation	$	55,283		$	63,417		$	3,131		$	3,427		$	5,850		$	6,766
Components of Net Periodic Expense (dollars in thousands)
	Defined Benefit Pension Plan									Supplemental Non-qualified Defined Benefit Retirement Plans									Non-pension Defined Benefit Postretirement Healthcare Plan
	2013			2012			2011			2013			2012			2011			2013			2012			2011
Service cost	$	852		$	765		$	798		$	—		$	—		$	—		$	216		$	214		$	210
Interest cost	2,969			2,969			3,092			133			104			114			239			343			365
Expected return on assets	(3,764		)	(3,139		)	(3,619		)	—			—			—			—			—			—
Amortization of prior service cost (credits)	43			57			62			—			—			—			(278		)	(278		)	(314		)
Amortization of transition obligation	2,609			—			—			—			—			—			—			—			—
Recognized net actuarial loss (gain)	—			2,599			1,486			66			55			48			9			139			163
Curtailment expense	—			—			—			—			—			—			—			—			—
Net periodic expense	$	2,709		$	3,251		$	1,819		$	199		$	159		$	162		$	186		$	418		$	424
Accumulated Other Comprehensive Income (Loss)
Amounts included in AOCI, after-tax, that have not yet been recognized as components of net periodic benefit cost at December 31 were as follows (in thousands):
	Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
	2013			2012			2013			2012			2013			2012
Net loss	$	—		$	—		$	(479	)	$	(660	)	$	—		$	—
Prior service cost	—			—			—			—			—			—
Total accumulated other comprehensive income (loss)	$	—		$	—		$	(479	)	$	(660	)	$	—		$	—
The amounts in AOCI, regulatory assets or regulatory liabilities, after-tax, expected to be recognized as a component of net periodic benefit cost during calendar year 2014 were as follows (in thousands):
	Defined Benefits Pension Plan			Supplemental Non-qualified Defined Benefit Retirement Plans			Non-pension Defined Benefit Postretirement Healthcare Plan
Net loss	$	611		$	29		$	—
Prior service cost	28			—			(206		)
Total net periodic benefit cost expected to be recognized during calendar year 2014	$	639		$	29		$	(206	)
Assumptions
	Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
	2013		2012		2011		2013		2012		2011		2013		2012		2011
Weighted-average assumptions used to determine benefit obligations:
Discount rate	5.1	%	4.35	%	4.65	%	4.68	%	4.25	%	4.7	%	4.45	%	3.65	%	4.35	%
Rate of increase in compensation levels	3.86	%	3.91	%	3.67	%	N/A		N/A		N/A		N/A		N/A		N/A
Weighted-average assumptions used to determine net periodic benefit cost for plan year:
Discount rate	4.35	%	4.65	%	5.5	%	3.88	%	4.7	%	5	%	3.65	%	4.35	%	5	%
Expected long-term rate of return on assets*	7.25	%	7.25	%	7.75	%	N/A		N/A		N/A		N/A		N/A		N/A
Rate of increase in compensation levels	3.91	%	3.67	%	3.7	%	N/A		N/A		N/A		N/A		N/A		N/A
_____________________________
*	The expected rate of return on plan assets is 6.75% for the calculation of the 2014 net periodic pension cost.
The healthcare benefit obligation was determined at December 31 as follows:
	2013		2012
Healthcare trend rate pre-65
Trend for next year	7.5	%	7.75	%
Ultimate trend rate	4.5	%	4.5	%
Year Ultimate Trend Reached	2027		2027
Healthcare trend rate post-65
Trend for next year	6.25	%	6.5	%
Ultimate trend rate	4.5	%	4.5	%
Year Ultimate Trend Reached	2026		2026
We do not pre-fund our post-retirement benefit plan. The table below shows the estimated impacts of an increase or decrease to our healthcare trend rate for our Retiree Health Care Plan (dollars in thousands):
Change in Assumed Trend Rate	Service and Interest Costs			Accumulated Periodic Postretirement Benefit Obligation
1% increase	$	9		$	179
1% decrease	$	(9	)	$	(165	)
The following benefit payments, which reflect future service, are expected to be paid (in thousands):
	Defined Benefit Pension Plan			Supplemental Non-qualified Defined Benefit Retirement Plans			Non-pension Defined Benefit Postretirement Healthcare Plan
2014	$	3,177		$	217		$	491
2015	$	3,227		$	214		$	432
2016	$	3,270		$	184		$	410
2017	$	3,367		$	213		$	418
2018	$	3,483		$	210		$	473
2019-2023	$	20,002		$	1,271		$	2,483
Defined Contribution Plan
The Parent sponsors a 401(k) retirement savings plan in which our employees may participate. Participants may elect to invest up to 50% of their eligible compensation on a pre-tax or after-tax basis, up to a maximum amount established by the Internal Revenue Service. The plan provides for company matching contributions and company retirement contributions. Employer contributions vest at 20% per year and are fully vested when the participant has 5 years of service.

Related_Party_Transactions_Not

Related Party Transactions (Notes)	12 Months Ended
	Dec. 31, 2013
Related Party Transactions [Abstract]	'
Related Party Transactions Disclosure [Text Block]	'
	RELATED-PARTY TRANSACTIONS
	Non-Cash Dividend to Parent
	We have recorded a non-cash dividend to our Parent for approximately $8.0 million and $44 million in 2013 and 2012 and decreased the utility money pool note receivable, net for approximately $8.0 million and $44 million, in 2013 and 2012 respectively.
	Receivables and Payables
	We have accounts receivable and accounts payable balances related to transactions with other BHC subsidiaries. These balances as of December 31 were as follows (in thousands):
		2013		2012
	Receivable - affiliates	$	4,934	$	5,027
	Accounts payable - affiliates	$	21,082	$	21,896
	Money Pool Notes Receivable and Notes Payable
	We have a Utility Money Pool Agreement (the Agreement) with BHC, Cheyenne Light and Black Hills Energy. Under the agreement, we may borrow from BHC however the Agreement restricts us from loaning funds to BHC or to any of BHCs’ non-utility subsidiaries. The Agreement does not restrict us from making dividends to BHC. Borrowings under the agreement bear interest at the weighted average daily cost of our parent company’s credit facility borrowings as defined under the Agreement, or if there are no external funds outstanding on that date, then the rate will be the daily one month LIBOR rate plus 1.0%.
	The cost of borrowing under the Utility Money Pool was 1.60% at December 31, 2013.
	We had the following balances with the Utility Money Pool as of December 31 (in thousands):
		2013		2012
	Notes receivable (payable), net	$	17,292	$	31,645
	Net interest income (expense) relating to the Utility Money Pool for the years ended December 31, was as follows (in thousands)
		2013		2012		2011
	Net interest income (expense)	$	505	$	617	$	1,414
	Other Balances and Transactions
	We have the following Power Purchase and Transmission Services Agreements with affiliated entities:
	•	Cheyenne Light entered into a PPA with Happy Jack. Under a separate inter-company agreement expiring on September 3, 2028, Cheyenne Light has agreed to sell up to 15 MW of the facility output from Happy Jack to us.
	•	Cheyenne Light entered into a PPA with Silver Sage. Under a separate inter-company agreement expiring on September 30, 2029, Cheyenne Light has agreed to sell 20 MW of energy from Silver Sage to us.
	•	A Generation Dispatch Agreement with Cheyenne Light that requires us to purchase all of Cheyenne Light’s excess energy.
	We had the following related party transactions for the years ended December 31 included in the corresponding captions in the accompanying Statements of Income:
		2013		2012		2011
		(in thousands)
	Revenues:
	Energy sold to Cheyenne Light	$	1,338	$	2,372	$	957
	Rent from electric properties	$	3,627	$	2,661	$	7,523
	Purchases:
	Purchase of coal from WRDC	$	18,542	$	20,690	$	21,319
	Purchase of excess energy from Cheyenne Light	$	3,640	$	3,139	$	4,127
	Purchase of renewable wind energy from Cheyenne Light - Happy Jack	$	1,886	$	1,988	$	1,955
	Purchase of renewable wind energy from Cheyenne Light - Silver Sage	$	3,207	$	3,269	$	3,281
	Corporate support services from Parent, Black Hills Service Company and Black Hills Utility Holdings	$	30,738	$	24,163	$	18,567

Supplemental_Cash_Flows_Inform

Supplemental Cash Flows Information (Notes)	12 Months Ended
	Dec. 31, 2013
Supplemental Cash Flow Information [Abstract]	'
Cash Flow, Supplemental Disclosures [Text Block]	'
	SUPPLEMENTAL CASH FLOW INFORMATION
	Years ended December 31,	2013			2012			2011
		(in thousands)
	Non-cash investing and financing activities -
	Property, plant and equipment acquired with accrued liabilities	$	13,590		$	3,969		$	1,882
	Non-cash decrease to money pool note receivable, net	$	(8,000	)	$	(43,984	)	$	—
	Non-cash dividend to Parent company	$	8,000		$	43,984		$	—
	Supplemental disclosure of cash flow information:
	Cash (paid) refunded during the period for -
	Interest (net of amounts capitalized)	$	(19,174	)	$	(17,099	)	$	(16,294	)
	Income taxes	$	219		$	7,176		$	(15,347	)

Commitment_and_Contingencies_N

Commitment and Contingencies (Notes)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies Disclosure [Text Block]	'
	COMMITMENTS AND CONTINGENCIES
	Power Purchase and Transmission Services Agreements
	We have the following power purchase and transmission agreements, not including related party agreements, as of December 31, 2013 (see Note 9 for information on related party agreements):
	•	A PPA with PacifiCorp expiring on December 31, 2023, which provides for the purchase by us of 50 MW of electric capacity and energy. The price paid for the capacity and energy is based on the operating costs of one of PacifiCorp’s coal-fired electric generating plants;
	•	A firm point-to-point transmission access agreement to deliver up to 50 MW of power on PacifiCorp’s transmission system to wholesale customers in the western region through December 31, 2023; and
	•	An agreement with Thunder Creek for gas transport capacity, expiring in October 31, 2019.
	Costs incurred under these agreements were as follows for the years ended December 31 (in thousands):
	Contract	Contract Type	2013		2012		2011
	PacifiCorp	Electric capacity and energy	$	13,026	$	13,224	$	12,515
	PacifiCorp	Transmission access	$	1,384	$	1,215	$	1,215
	Thunder Creek	Gas transport capacity	$	633	$	633	$	633
	Future Contractual Obligations
	The following is a schedule of future minimum payments required under the power purchase, transmission services, facility and vehicle leases, and gas supply agreements (in thousands):
	2014	$	12,451
	2015	$	12,443
	2016	$	12,443
	2017	$	12,443
	2018	$	6,133
	Thereafter	$	28,764
	Long-Term Power Sales Agreements
	We have the following power sales agreements as of December 31, 2013:
	•	During periods of reduced production at Wygen III in which MDU owns a portion of the capacity, or during periods when Wygen III is off-line, MDU will be provided with 25 MW from our other generation facilities or from system purchases with reimbursement of costs by MDU;
	•	During periods of reduced production at Wygen III in which the City of Gillette owns a portion of the capacity, or during periods when Wygen III is off-line, we will provide the City of Gillette with its first 23 MW from our other generating facilities or from system purchases with reimbursement of costs by the City of Gillette. Under this agreement, Black Hills Power will also provide the City of Gillette their operating component of spinning reserves;
	•	An agreement under which we supply energy and capacity to MEAN expiring on May 31, 2023. This contract is unit-contingent based on up to 10 MW from our Neil Simpson II and up to 10 MW from our Wygen III plants. The energy and capacity purchase requirements decrease over the term of the agreement; and
	•	A PPA with MEAN, expiring on April 1, 2015. Under this contract, MEAN purchases 5 MW of unit-contingent energy and capacity from Neil Simpson II and 5 MW of unit-contingent capacity from Wygen III.
	Oil Creek Fire
	On June 29, 2012, a forest and grassland fire occurred in the western Black Hills of Wyoming. A fire investigator concluded that the fire was caused by the failure of a transmission structure owned, operated and maintained by us. On April 16, 2013, thirty-five private parties filed suit in the United States District Court for the District of Wyoming, asserting claims for damages against us based upon allegations of negligence, negligence per se, common law nuisance, and trespass. Although not currently included in the lawsuit, we also received written damage claims from an additional landowner and from the State of Wyoming. Altogether the claims seek recovery for fire suppression, reclamation and rehabilitation costs, damage to fencing and other personal property, alleged injury to timber, grass or hay, livestock and related operations, and diminished value of real estate, for a current total amount of $15 million. In addition to claims for these compensatory damages, the lawsuit seeks recovery of punitive damages. Our investigation of the cause and origin of the fire is ongoing. We have denied and will vigorously defend all claims arising out of the fire, pending the completion of our investigation. Given the uncertainty of litigation, however, a loss related to the fire, the litigation and related claims, is reasonably possible. We cannot reasonably estimate the amount of a potential loss because our investigation is ongoing, and because damage claims are currently incomplete or undocumented. Further claims may be presented by these and other parties. We cannot predict the outcome of our investigation, the viability of alleged claims or the outcome of the litigation. Based upon information currently available, however, management does not expect the claims, if determined adversely to us, to have a material adverse effect upon our financial condition, results of operations or cash flows.
	Legal Proceedings
	We are subject to various legal proceedings, claims and litigation which arise in the ordinary course of operations. In the opinion of management, the amount of liability, if any, with respect to these actions would not materially affect our financial position, results of operations or cash flows.
	In the normal course of business, we enter into agreements that include indemnification in favor of third parties, such as information technology agreements, purchase and sale agreements and lease contracts. We have also agreed to indemnify our directors, officers and employees in accordance with our articles of incorporation, as amended. Certain agreements do not contain any limits on our liability and therefore, it is not possible to estimate our potential liability under these indemnifications. In certain cases, we have recourse against third parties with respect to these indemnities. Further, we maintain insurance policies that may provide coverage against certain claims under these indemnities.
	Environmental Matters
	We are subject to costs resulting from a number of federal, state and local laws and regulations which affect future planning and existing operations. They can result in increased capital expenditures, operating and other costs as a result of compliance, remediation and monitoring obligations. Due to the environmental issues discussed below, we may be required to modify, curtail, replace or cease operating certain facilities or operations to comply with statutes, regulations and other requirements of regulatory bodies.
	Air
	Our generation facilities are subject to federal, state and local laws and regulations relating to the protection of air quality. These laws and regulations cover, among other pollutants, carbon monoxide, SO2, NOx, mercury particulate matter and GHG. Power generating facilities burning fossil fuels emit each of the foregoing pollutants and, therefore, are subject to substantial regulation and enforcement oversight by various governmental agencies.
	Title IV of the Clean Air Act applies to several of our generation facilities, including the Neil Simpson II, Neil Simpson CT II, Lange CT, Wygen III and Wyodak plants. Title IV of the Clean Air Act created an SO2 allowance trading program as part of the federal acid rain program. Without purchasing additional allowances, we currently hold sufficient allowances to satisfy Title IV at all such plants through 2042.
	The EPA issued the Industrial and Commercial Boiler Regulations for Area Sources of Hazardous Air Pollutants, with updates which impose emission limits, fuel requirements and monitoring requirements. The rule has a compliance deadline of March 21, 2014. In anticipation of this rule, we suspended operations at the Osage plant on October 1, 2010 and as a result of this rule, we suspended operations at the Ben French facility on August 31, 2012 with plans to retire Osage, Ben French and Neil Simpson I on or before March 21, 2014. While the net book value of these plants is estimated to be insignificant at the time of retirement, we would reasonably expect any remaining value to be recovered through future rates.
	Solid Waste Disposal
	Various materials used at our facilities are subject to disposal regulations. Our Osage plant, at which operations have been suspended, has an on-site ash impoundment that is near capacity. An application to close the impoundment was approved by the State of Wyoming on April 13, 2012. Site closure work was completed in 2013 and post closure monitoring activities will continue for 30 years. In September 2013, Osage also received a permit to close the small industrial rubble landfill. Site work was completed and post closure monitoring will continue for 30 years.

Quarterly_Historical_Data_Unau

Quarterly Historical Data (Unaudited)	12 Months Ended
	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]	'
Quarterly Financial Information [Text Block]	'
	QUARTERLY HISTORICAL DATA (Unaudited)
	We operate on a calendar year basis. The following table sets forth selected unaudited historical operating results data for each quarter (in thousands):
		First		Second		Third		Fourth
		Quarter		Quarter		Quarter		Quarter
	2013
	Operating revenues	$	59,817	$	60,832	$	67,268	$	66,110
	Operating income	$	12,503	$	14,293	$	18,704	$	16,844
	Net income	$	5,582	$	6,652	$	9,298	$	8,641
	2012
	Operating revenues	$	62,270	$	58,372	$	61,134	$	61,533
	Operating income	$	12,742	$	13,859	$	15,361	$	15,619
	Net income	$	6,053	$	6,727	$	8,147	$	6,159

Schedule_II_Schedule_of_Valuat

Schedule II - Schedule of Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2013
Valuation and Qualifying Accounts [Abstract]	'
Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	'
	BLACK HILLS POWER, INC.
	VALUATION AND QUALIFYING ACCOUNTS
	YEARS ENDED DECEMBER 31,
	Description	Balance at beginning of year		Additions charged to costs and expenses		Deductions charged to costs and expenses			Balance at end of year
		(in thousands)
	Allowance for doubtful accounts:
	2013	$	102	$	754	$	(636	)	$	220
	2012	$	143	$	503	$	(544	)	$	102
	2011	$	230	$	551	$	(638	)	$	143

Business_Description_Policies

Business Description (Policies)	12 Months Ended
	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Basis of Accounting, Policy [Policy Text Block]	'
	Basis of Presentation
	The financial statements include the accounts of Black Hills Power, Inc. and also our ownership interests in the assets, liabilities and expenses of our jointly owned facilities (Note 3) and are prepared in accordance with GAAP.
Use of Estimates, Policy [Policy Text Block]	'
	Use of Estimates and Basis of Presentation
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Cash and Cash Equivalents, Policy [Policy Text Block]	'
	Cash Equivalents
	We consider all highly liquid investments with an original maturity of three months or less to be cash equivalents.
Public Utilities, Policy [Policy Text Block]	'
	Regulatory Accounting
	Our regulated electric operations are subject to regulation by various state and federal agencies. The accounting policies followed are generally subject to the Uniform System of Accounts of FERC.
	Our regulated utility operations follow accounting standards for regulated operations and our financial statements reflect the effects of the different rate making principles followed by the various jurisdictions regulating our electric operations. If rate recovery becomes unlikely or uncertain due to competition or regulatory action, these accounting standards may no longer apply to our regulated operations. In the event we determine that we no longer meet the criteria for following accounting standards for regulated operations, the accounting impact to us could be an extraordinary non-cash charge to operations in an amount that could be material.
	Regulatory assets are included in Regulatory assets, current and Regulatory assets, non-current on the accompanying Balance Sheets. Regulatory liabilities are included in Regulatory liabilities, current and Regulatory liabilities, non-current on the accompanying Balance Sheets.
Trade and Other Accounts Receivable, Policy [Policy Text Block]	'
	Accounts Receivable and Allowance for Doubtful Accounts
	Accounts receivable consist of sales to residential, commercial, industrial, municipal and other customers all of which do not bear interest. These accounts receivable are stated at billed and unbilled amounts net of write-offs or payment received.
	We maintain an allowance for doubtful accounts which reflects our best estimate of uncollectible trade receivables. We regularly review our trade receivable allowances by considering such factors as historical experience, credit worthiness, the age of the receivable balances and current economic conditions that may affect collectibility. The allowance is calculated by applying estimated write-off factors to various classes of outstanding receivables, including unbilled revenue. The write-off factors used to estimate uncollectible accounts are based upon consideration of both historical collections experience and management’s best estimate of future collection success given the existing collections environment.
Revenue Recognition, Policy [Policy Text Block]	'
	Revenue Recognition
	Revenue is recognized when there is persuasive evidence of an arrangement with a fixed or determinable price, delivery has occurred or services have been rendered, and collectibility is reasonably assured. Taxes collected from our customers are recorded on a net basis (excluded from Revenue).
	Utility revenues are based on authorized rates approved by the state regulatory agencies and the FERC. Revenues related to the sale, transmission and distribution of energy, and delivery of service are generally recorded when service is rendered or energy is delivered to customers. To the extent that deliveries have occurred but a bill has not been issued, we accrue an estimate of the revenue since the latest billing. This estimate is calculated based upon several factors including billings through the last billing cycle in a month, and prices in effect in our jurisdictions. Each month the estimated unbilled revenue amounts are trued-up and recorded in Receivables- customers, net on the accompanying Balance Sheets.
Inventory, Policy [Policy Text Block]	'
	Materials, Supplies and Fuel
	Materials, supplies and fuel used for construction, operation and maintenance purposes are generally stated on a weighted-average cost basis.
Debt, Policy [Policy Text Block]	'
	Deferred Financing Costs
	Deferred financing costs are amortized using the effective interest method over the term of the related debt.
Property, Plant and Equipment, Policy [Policy Text Block]	'
	Property, Plant and Equipment
	Additions to property, plant and equipment are recorded at cost when placed in service. Included in the cost of regulated construction projects is AFUDC, which represents the approximate composite cost of borrowed funds and a return on equity used to finance a regulated utility project. The cost of regulated electric property, plant and equipment retired, or otherwise disposed of in the ordinary course of business, less salvage, is charged to accumulated depreciation. Removal costs associated with non-legal obligations are reclassified from accumulated depreciation and reflected as regulatory liabilities. Ordinary repairs and maintenance of property, except as allowed under rate regulations, are charged to operations as incurred.
	Depreciation provisions for regulated electric property, plant and equipment are computed on a straight-line basis using an annual composite rate of 2.1% in 2013, 2.2% in 2012 and 2.2% in 2011.
Derivatives, Policy [Policy Text Block]	'
	Derivatives and Hedging Activities
	From time to time we utilize risk management contracts including forward purchases and sales to hedge the price of fuel for our combustion turbines and fixed-for-float swaps to fix the interest on any variable rate debt. Contracts that qualify as derivatives under accounting standards for derivatives, and that are not exempted such as normal purchase/normal sale, are required to be recorded in the balance sheet as either an asset or liability, measured at its fair value. Accounting standards for derivatives require that changes in the derivative instrument’s fair value be recognized currently in earnings unless specific hedge accounting criteria are met.
	Accounting standards for derivatives allow hedge accounting for qualifying fair value and cash flow hedges. Gain or loss on a derivative instrument designated and qualifying as a fair value hedging instrument as well as the offsetting loss or gain on the hedged item attributable to the hedged risk should be recognized currently in earnings in the same accounting period. Conversely, the effective portion of the gain or loss on a derivative instrument designated and qualifying as a cash flow hedging instrument should be reported as a component of other comprehensive income and be reclassified into earnings or as a regulatory asset or regulatory liability, net of tax, in the same period or periods during which the hedged forecasted transaction affects earnings. The remaining gain or loss on the derivative instrument, if any, is recognized currently in earnings.
Fair Value of Financial Instruments, Policy [Policy Text Block]	'
	Fair Value Measurements
	Accounting standards for fair value measurements provide a single definition of fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date and also requires disclosures and establishes a fair value hierarchy that prioritizes the inputs used to measure fair value. The fair value hierarchy ranks the quality and reliability of the information used to determine fair values giving the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements).
	Financial assets and liabilities carried at fair value are classified and disclosed in one of the following three categories:
	Level 1 - Unadjusted quoted prices available in active markets that are accessible at the measurement date for identical unrestricted assets or liabilities.
	Level 2 - Pricing inputs include quoted prices for identical or similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and inputs that are derived principally from or corroborated by observable market data by correlation or other means.
	Level 3 - Pricing inputs include significant inputs that are generally less observable from objective sources.
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]	'
	Impairment of Long-Lived Assets
	We periodically evaluate whether events and circumstances have occurred which may affect the estimated useful life or the recoverability of the remaining balance of our long-lived assets. If such events or circumstances were to indicate that the carrying amount of these assets was not recoverable, we would estimate the future cash flows expected to result from the use of the assets and their eventual disposition. If the sum of the expected future cash flows (undiscounted and without interest charges) was less than the carrying amount of the long-lived assets, we would recognize an impairment loss.
Income Tax, Policy [Policy Text Block]	'
	Income Taxes
	We file a federal income tax return with other members of the Parent’s consolidated group. For financial statement purposes, federal income taxes are allocated to the individual companies based on amounts calculated on a separate return basis.
	We use the liability method in accounting for income taxes. Under the liability method, deferred income taxes are recognized at currently enacted income tax rates, to reflect the tax effect of temporary differences between the financial and tax basis of assets and liabilities, as well as operating loss and tax credit carryforwards. Such temporary differences are the result of provisions in the income tax law that either require or permit certain items to be reported on the income tax return in a different period than they are reported in the financial statements. We classify deferred tax assets and liabilities into current and non-current amounts based on the classification of the related assets and liabilities.
	It is the Parent’s policy to apply the flow-through method of accounting for investment tax credits. Under the flow-through method, investment tax credits are reflected in net income as a reduction to income tax expense in the year they qualify. Another acceptable accounting method and an exception to this general policy is to apply the deferral method whereby the credit is amortized as a reduction of income tax expense over the useful lives of the related property which gave rise to the credits.
	We recognize interest income or interest expense and penalties related to income tax matters in Income tax (expense) benefit on the Statements of Income. We account for uncertainty in income taxes recognized in the financial statements in accordance with accounting standards for income taxes. The unrecognized tax benefit is classified in Other - non-current liabilities on the accompanying Balance Sheets.

Business_Description_Tables

Business Description (Tables)	12 Months Ended
	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Schedule of Regulatory Assets and Liabilities [Table Text Block]	'
	We had the following regulatory assets and liabilities as follows as of December 31 (in thousands):
		Maximum Recovery Period (in years)	2013			2012
	Regulatory assets:
	Unamortized loss on reacquired debt(a)	14	$	2,257		$	2,501
	AFUDC(b)	45	8,327			8,460
	Employee benefit plans(c)	13	15,233			27,001
	Deferred energy costs(a)	1	7,711			6,892
	Flow through accounting(a)	35	9,723			8,019
	Other regulatory assets(a)	2	2,013			369
	Total regulatory assets		$	45,264		$	53,242
	Regulatory liabilities:
	Cost of removal for utility plant(a)	53	$	30,467		$	26,630
	Employee benefit plans(d)	13	10,177			15,689
	Other regulatory liabilities(e)	13	2,874			1,567
	Total regulatory liabilities		$	43,518		$	43,886
	____________________
	(a)    Recovery of costs but not allowed a rate of return.
	(b)	In addition to recovery of costs, we are allowed a rate of return.
	(c)	In addition to recovery of costs, we are allowed a return on approximately $24 million according to the approved rate case.
	(d)	Approximately $13 million is included in our rate base calculation as a reduction to rate base.
	(e)	Approximately $0.8 million is included in our rate base calculation as a reduction to rate base
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]	'
	Following is a summary of accounts receivable at December 31 (in thousands):
		2013			2012
	Accounts receivable trade	$	16,300		$	14,965
	Unbilled revenues	9,719			9,004
	Allowance for doubtful accounts	(220		)	(102		)
	Net accounts receivable	$	25,799		$	23,867

Propety_Plant_Equipment_tables

Propety Plant Equipment (tables)	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment [Table Text Block]	'
	Property, plant and equipment at December 31 consisted of the following (dollars in thousands):
					2013				2012
					Weighted				Weighted
					Average				Average	Lives (in years)
		2013			Useful Life (in years)	2012			Useful Life (in years)	Minimum	Maximum
	Electric plant:
	Production	$	512,444		51	$	510,674		51	45	65
	Transmission	115,149			46	115,092			46	40	60
	Distribution	315,971			39	304,113			38	16	45
	Plant acquisition adjustment (a)	4,870			32	4,870			32	32	32
	General	70,228			22	71,802			22	8	45
	Total plant-in-service	1,018,662				1,006,551
	Construction work in progress	77,222				18,217
	Total electric plant	1,095,884				1,024,768
	Less accumulated depreciation and amortization	(334,174		)		(322,830		)
	Electric plant net of accumulated depreciation and amortization	$	761,710			$	701,938
	__________________
	(a)	The plant acquisition adjustment is included in rate base and is being recovered with 17 years remaining.

Jointly_Owned_Facilities_table

Jointly Owned Facilities (tables)	12 Months Ended
	Dec. 31, 2013
Jointly Owned Utility Plant, Net Ownership Amount [Abstract]	'
Schedule Of Jointly Owned Facilities [Table Text Block]	'
	As of December 31, 2013, our interests in jointly-owned generating facilities and transmission systems included on our Balance Sheets were as follows (in thousands):
	Interest in jointly-owned facilities	Plant in Service		Construction Work in Progress		Accumulated Depreciation
	Wyodak Plant	$	109,800	$	192	$	50,595
	Transmission Tie	$	19,648	$	—	$	4,741
	Wygen III	$	131,468	$	713	$	10,593

Long_Term_Debt_Tables

Long Term Debt (Tables)	12 Months Ended
	Dec. 31, 2013
Long-term Debt, Unclassified [Abstract]	'
Schedule of Long-term Debt Instruments [Table Text Block]	'
	Long-term debt outstanding at December 31 was as follows (in thousands):
		Maturity Date	Interest Rate		2013			2012
	First Mortgage Bonds due 2032	August 15, 2032	7.23	%	$	75,000		$	75,000
	First Mortgage Bonds due 2039	November 1, 2039	6.125	%	180,000			180,000
	Unamortized discount, First Mortgage Bonds due 2039				(107		)	(111		)
	Pollution control revenue bonds due 2024	October 1, 2024	5.35	%	12,200			12,200
	Series 94A Debt(a)	June 1, 2024	0.75	%	2,855			2,855
	Long-term debt				$	269,948		$	269,944
	___________________
	(a)	Variable interest rate at December 31, 2013.
Schedule of Maturities of Long-term Debt [Table Text Block]	'
	Scheduled maturities of our outstanding long-term debt (excluding unamortized discounts) are as follows (in thousands):
	2014	$	—
	2015	$	—
	2016	$	—
	2017	$	—
	2018	$	—
	Thereafter	$	270,055

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value of Financial Instruments	'
	The estimated fair values of our financial instruments at December 31 were as follows (in thousands):
		2013				2012
		Carrying Value		Fair Value		Carrying Value		Fair Value
	Cash and cash equivalents (a)	$	2,259	$	2,259	$	3,805	$	3,805
	Long-term debt, including current maturities (b)	$	269,948	$	317,531	$	269,944	$	359,567
	_______________
	(a)	Fair value approximates carrying value due to either short-term length of maturity or variable interest rates that approximate prevailing market rates and therefore is classified in Level 1 in the fair value hierarchy.
	(b)	Long-term debt is valued using the market approach based on observable inputs of quoted market prices and yields available for debt instruments either directly or indirectly for similar maturities and debt ratings in active markets and therefore is classified in Level 2 in the fair value hierarchy. The carrying amount of our variable rate debt approximates fair value due to the variable interest rates with short reset periods. For additional information on our long-term debt, see Note 4 to the Financial Statements.

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	'
	Income tax expense (benefit) from continuing operations for the years ended December 31 were as follows (in thousands):
		2013			2012			2011
	Current	$	(163	)	$	(10,319	)	$	14,921
	Deferred	13,582			24,628			(2,931		)
	Total income tax expense	$	13,419		$	14,309		$	11,990
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	'
	The temporary differences which gave rise to the net deferred tax liability, for the years ended December 31 were as follows (in thousands):
		2013			2012
	Deferred tax assets:
	Employee benefits	$	4,567		$	5,094
	Net operating loss	4,197			10,441
	Regulatory liabilities	6,398			13,433
	Other	2,193			2,381
	Total deferred tax assets	17,355			31,349
	Deferred tax liabilities:
	Accelerated depreciation and other plant related differences	(161,990		)	(154,989		)
	AFUDC	(8,190		)	(5,499		)
	Regulatory assets	(3,540		)	(5,767		)
	Employee benefits	(3,467		)	(3,610		)
	Deferred costs	(4,240		)	(2,608		)
	Other	(1,067		)	(1,163		)
	Total deferred tax liabilities	(182,494		)	(173,636		)
	Net deferred tax assets (liabilities)	$	(165,139	)	$	(142,287	)
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	'
	The effective tax rate differs from the federal statutory rate for the years ended December 31, as follows:
		2013		2012		2011
	Federal statutory rate	35	%	35	%	35	%
	Amortization of excess deferred and investment tax credits	(0.3	)	(0.3	)	(0.4	)
	Equity AFUDC	—		(0.1	)	(0.6	)
	Flow through adjustments *	(2.5	)	(3.5	)	(3.4	)
	Prior year deferred adjustment **	—		3.6		—
	Tax credits	(0.8	)	—		—
	Other	(0.6	)	(0.1	)	0.1
		30.8	%	34.6	%	30.7	%
	_________________________
	*	The flow-through adjustments relate primarily to an accounting method change for tax purposes that allows us to take a current tax deduction for repair costs that continue to be capitalized for book purposes. We recorded a deferred income tax liability in recognition of the temporary difference created between book and tax treatment and we flowed the tax benefit through to our customers in the form of lower rates as a result of a rate case settlement that occurred during 2010. A regulatory asset was established to reflect the recovery of future increases in taxes payable from customers as the temporary differences reverse. As a result of this regulatory treatment, we continue to record a tax benefit consistent with the flow through method.
	**	The adjustment was a non-recurring unfavorable true-up attributable to property related deferred income taxes. The removal of the impact of such an adjustment is more appropriately reflective of the effective rate on a recurring basis.
Summary of Deferred Tax Liability Not Recognized [Table Text Block]	'
	The following table reconciles the total amounts of unrecognized tax benefits, without interest, included in Other deferred credits and other liabilities on the accompanying Balance Sheet (in thousands):
		2013			2012
	Unrecognized tax benefits at January 1	$	2,078		$	3,595
	Reductions for prior year tax positions	(155		)	(1,586		)
	Additions for current year tax positions	520			69
	Unrecognized tax benefits at December 31	$	2,443		$	2,078

Comprehensive_Income_Loss_Tabl

Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	'
	(in thousands):
		Derivatives Designated as Cash Flow Hedges	Amounts Reclassified from AOCI
			2013			2012
	Gains and Losses on cash flow hedges
	Interest rate swaps	Interest expense	$	64		$	64
	Income tax	Income tax benefit (expense)	(23		)	(23		)
	Total reclassification adjustments related to cash flow hedges, net of tax		$	41		$	41
	Amortization of defined benefit plans:
	Actuarial gain (loss)	Operations and maintenance	$	66		$	—
	Income tax	Income tax benefit (expense)	(23		)	—
	Total reclassification adjustments related to defined benefit plans, net of tax		$	43		$	—
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	'
	Balances by classification included within Accumulated other comprehensive loss on the accompanying Balance Sheets were as follows (in thousands):
		Derivatives Designated as Cash Flow Hedges
		Interest Rate Swaps			Employee Benefit Plans			Total
	As of December 31, 2012	$	(760	)	$	(660	)	$	(1,420	)
	Other comprehensive income (loss)	41			182			223
	As of December 31, 2013	$	(719	)	$	(478	)	$	(1,197	)
		Derivatives Designated as Cash Flow Hedges
		Interest Rate Swaps			Employee Benefit Plans			Total
	As of December 31, 2011	$	(801	)	$	(489	)	$	(1,290	)
	Other comprehensive income (loss)	41			(171		)	(130		)
	As of December 31, 2012	$	(760	)	$	(660	)	$	(1,420	)

Employee_Benefit_Plans_Employe

Employee Benefit Plans Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]	'
Schedule of Allocation of Plan Assets [Table Text Block]	'
	The percentages of total plan asset fair value by investment category of our Pension Plan assets at December 31 were as follows:
		2013		2012
	Equity securities	26	%	51	%
	Real estate	4	%	—	%
	Fixed income funds	58	%	48	%
	Cash and cash equivalents	1	%	1	%
	Hedge funds	11	%	—	%
	Total	100	%	100	%
Schedule of Contribution to Employee Plans [Table Text Block]	'
	Contributions for the years ended December 31 were as follows (in thousands):
		2013			2012
	Defined Benefit Plans
	Defined Benefit Pension Plan	$	2,299		$	6,835
	Non-pension Defined Benefit Postretirement Healthcare Plan	$	578		$	835
	Supplemental Non-qualified Defined Benefit Plan	$	217		$	256
	Defined Contribution Plans
	Company Retirement Contribution	$	421		$	404
	Matching Contributions	$	1,301		$	1,328
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]	'
	The following table sets forth a summary of changes in the fair value of the Defined Benefit Pension Plans’ Level 3 assets for the period ended December 31 (in thousands):
		2013
	Balance, beginning of period	$	—
	Transfers	1,550
	Purchase	5,834
	Unrealized gain (loss)	317
	Realized gain (loss)	(3		)
	Settlements	(15		)
	Balance, end of period	$	7,683
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table Text Block]	'
	The following table presents the quantitative information about Level 3 fair value measurements (dollars in thousands):
		Fair Value at			Valuation	Level 3	Range (Weighted)
		31-Dec-13			Technique	Input	Average
	Assets:
	Common Collective Trust - Real Estate (a)	$	1,718		Market Approach	Redemption Restriction	N/A
	Hedge Funds (b)	$	5,965		Market Approach	Redemption Restriction	N/A
	_____________
	(a)	The underlying net asset value in the Common Collective Trust - Real Estate fund is determined by appraisal of the properties held in the Trust. As part of the Trustee's valuation process, properties are externally appraised generally on an annual basis. The appraisals are conducted by reputable independent appraisal firms and signed by appraisers that are members of the Appraisal Institute, with the professional designation of Member, Appraisal Institute. All external appraisals are performed in accordance with the Uniform Standards of Professional Appraisal Practices. We receive monthly statements from the Trustee along with the annual schedule of investments and rely on these reports for pricing the units of the fund. The fund does contain a participant withdrawal policy.
	(b)	The fair value of Level 3 is determined based on pricing provided or reviewed by third-party administrator to our investment managers. While the input amounts used by the pricing vendor in determining fair value are not provided, and therefore, unavailable for our review, the asset results are reviewed and monitored to ensure the fair values are reasonable and in line with market experience in similar asset classes. Additionally, the audited financial statements of the funds will be reviewed at the time they are issued.
Schedule of Changes in Projected Benefit Obligations [Table Text Block]	'
	The following tables provide a reconciliation of the Employee Benefit Plan’s obligations and fair value of assets, components of the net periodic expense and elements of regulatory assets and liabilities and AOCI (in thousands):
	Benefit Obligations
		Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
		2013			2012			2013			2012			2013			2012
	Change in benefit obligation:
	Projected benefit obligation at beginning of year	$	69,820		$	65,557		$	3,427		$	2,292		$	6,766		$	8,207
	Service cost	852			765			—			—			216			214
	Interest cost	2,969			2,969			133			104			239			343
	Actuarial loss (gain)	(7,818		)	4,510			(212		)	1,287			(459		)	(1,748		)
	Amendments (a)	—			—			—			—			(342		)	—
	Benefits paid	(4,850		)	(2,850		)	(217		)	(256		)	(1,045		)	(835		)
	Asset transfer (to) from affiliate	(750		)	(1,131		)	—			—			(75		)	26
	Plan curtailment reduction	—			—			—			—			—			—
	Medicare Part D adjustment	—			—			—			—			82			71
	Plan participants’ contributions	—			—			—			—			468			488
	Projected benefit obligation at end of year	$	60,223		$	69,820		$	3,131		$	3,427		$	5,850		$	6,766
	_______________
	(a)	Reflects Board of Directors approval of increase to Company’s contribution to RMSA account.
Schedule of Changes in Fair Value of Plan Assets [Table Text Block]	'
	A reconciliation of the fair value of Plan assets (as of the December 31 measurement date) is as follows (in thousands):
		Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
		2013			2012			2013			2012			2013			2012
	Beginning market value of plan assets	$	53,465		$	45,017		$	—		$	—		$	—		$	—
	Investment income	6,070			5,240			—			—			—			—
	Benefits paid	(4,850		)	(2,850		)	—			—			—			—
	Employer contributions	2,299			6,835			—			—			—			—
	Asset transfer to affiliate	(579		)	(777		)	—			—			—			—
	Ending market value of plan assets	$	56,405		$	53,465		$	—		$	—		$	—		$	—
Schedule of Amounts Recognized in Balance Sheet [Table Text Block]	'
	Amounts recognized in the Balance Sheets at December 31 consist of (in thousands):
		Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Plan
		2013			2012			2013			2012			2013			2012
	Regulatory asset (liability)	$	13,735		$	26,683		$	—		$	—		$	2,781		$	(2,174	)
	Current (liability)	$	—		$	—		$	(216	)	$	(216	)	$	(491	)	$	(438	)
	Non-current (liability)	$	(3,818	)	$	(16,356	)	$	(2,915	)	$	(3,211	)	$	(5,372	)	$	(6,321	)
Schedule of Accumulated and Projected Benefit Obligations [Table Text Block]	'
	Accumulated Benefit Obligation (dollars in thousands)
		Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
		2013			2012			2013			2012			2013			2012
	Accumulated benefit obligation	$	55,283		$	63,417		$	3,131		$	3,427		$	5,850		$	6,766
Schedule of Net Benefit Costs [Table Text Block]	'
	Components of Net Periodic Expense (dollars in thousands)
		Defined Benefit Pension Plan									Supplemental Non-qualified Defined Benefit Retirement Plans									Non-pension Defined Benefit Postretirement Healthcare Plan
		2013			2012			2011			2013			2012			2011			2013			2012			2011
	Service cost	$	852		$	765		$	798		$	—		$	—		$	—		$	216		$	214		$	210
	Interest cost	2,969			2,969			3,092			133			104			114			239			343			365
	Expected return on assets	(3,764		)	(3,139		)	(3,619		)	—			—			—			—			—			—
	Amortization of prior service cost (credits)	43			57			62			—			—			—			(278		)	(278		)	(314		)
	Amortization of transition obligation	2,609			—			—			—			—			—			—			—			—
	Recognized net actuarial loss (gain)	—			2,599			1,486			66			55			48			9			139			163
	Curtailment expense	—			—			—			—			—			—			—			—			—
	Net periodic expense	$	2,709		$	3,251		$	1,819		$	199		$	159		$	162		$	186		$	418		$	424
Schedule of Net Periodic Benefit Cost Not yet Recognized [Table Text Block]	'
	Amounts included in AOCI, after-tax, that have not yet been recognized as components of net periodic benefit cost at December 31 were as follows (in thousands):
		Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
		2013			2012			2013			2012			2013			2012
	Net loss	$	—		$	—		$	(479	)	$	(660	)	$	—		$	—
	Prior service cost	—			—			—			—			—			—
	Total accumulated other comprehensive income (loss)	$	—		$	—		$	(479	)	$	(660	)	$	—		$	—
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year [Table Text Block]	'
	The amounts in AOCI, regulatory assets or regulatory liabilities, after-tax, expected to be recognized as a component of net periodic benefit cost during calendar year 2014 were as follows (in thousands):
		Defined Benefits Pension Plan			Supplemental Non-qualified Defined Benefit Retirement Plans			Non-pension Defined Benefit Postretirement Healthcare Plan
	Net loss	$	611		$	29		$	—
	Prior service cost	28			—			(206		)
	Total net periodic benefit cost expected to be recognized during calendar year 2014	$	639		$	29		$	(206	)
Schedule of Assumptions Used [Table Text Block]	'
	Assumptions
		Defined Benefit Pension Plan						Supplemental Non-qualified Defined Benefit Retirement Plans						Non-pension Defined Benefit Postretirement Healthcare Plan
		2013		2012		2011		2013		2012		2011		2013		2012		2011
	Weighted-average assumptions used to determine benefit obligations:
	Discount rate	5.1	%	4.35	%	4.65	%	4.68	%	4.25	%	4.7	%	4.45	%	3.65	%	4.35	%
	Rate of increase in compensation levels	3.86	%	3.91	%	3.67	%	N/A		N/A		N/A		N/A		N/A		N/A
	Weighted-average assumptions used to determine net periodic benefit cost for plan year:
	Discount rate	4.35	%	4.65	%	5.5	%	3.88	%	4.7	%	5	%	3.65	%	4.35	%	5	%
	Expected long-term rate of return on assets*	7.25	%	7.25	%	7.75	%	N/A		N/A		N/A		N/A		N/A		N/A
	Rate of increase in compensation levels	3.91	%	3.67	%	3.7	%	N/A		N/A		N/A		N/A		N/A		N/A
	_____________________________
	*	The expected rate of return on plan assets is 6.75% for the calculation of the 2014 net periodic pension cost.
Schedule of Health Care Cost Trend Rates [Table Text Block]	'
	The healthcare benefit obligation was determined at December 31 as follows:
		2013		2012
	Healthcare trend rate pre-65
	Trend for next year	7.5	%	7.75	%
	Ultimate trend rate	4.5	%	4.5	%
	Year Ultimate Trend Reached	2027		2027
	Healthcare trend rate post-65
	Trend for next year	6.25	%	6.5	%
	Ultimate trend rate	4.5	%	4.5	%
	Year Ultimate Trend Reached	2026		2026
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]	'
	The table below shows the estimated impacts of an increase or decrease to our healthcare trend rate for our Retiree Health Care Plan (dollars in thousands):
	Change in Assumed Trend Rate	Service and Interest Costs			Accumulated Periodic Postretirement Benefit Obligation
	1% increase	$	9		$	179
	1% decrease	$	(9	)	$	(165	)
Schedule of Expected Benefit Payments [Table Text Block]	'
	The following benefit payments, which reflect future service, are expected to be paid (in thousands):
		Defined Benefit Pension Plan			Supplemental Non-qualified Defined Benefit Retirement Plans			Non-pension Defined Benefit Postretirement Healthcare Plan
	2014	$	3,177		$	217		$	491
	2015	$	3,227		$	214		$	432
	2016	$	3,270		$	184		$	410
	2017	$	3,367		$	213		$	418
	2018	$	3,483		$	210		$	473
	2019-2023	$	20,002		$	1,271		$	2,483
Pension Plan, Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Schedule of Allocation of Plan Assets [Table Text Block]	'
	The following tables set forth, by level within the fair value hierarchy, the assets that were accounted for at fair value on a recurring basis as of December 31 (in thousands):
	Defined Benefit Pension Plan	2013
		Level 1			Level 2			Level 3			Total Fair Value
	AXA Equitable General Fixed Income	$	—		$	213		$	—		$	213
	Common Collective Trust - Cash and Cash Equivalents	—			252			—			252
	Common collective trust - equity	—			14,833			—			14,833
	Common collective trust - fixed income	—			32,742			—			32,742
	Common collective trust - real estate	—			682			1,718			2,400
	Hedge funds	—			—			5,965			5,965
	Total investments measured at fair value	$	—		$	48,722		$	7,683		$	56,405
	Defined Benefit Pension Plan	2012
		Level 1			Level 2			Level 3			Total Fair Value
	Cash and cash equivalents	$	535		$	—		$	—		$	535
	Common collective trust - equity	—			27,267			—			27,267
	Common collective trust - fixed income	—			21,127			—			21,127
	Structured products	—			4,536			—			4,536
	Total investments measured at fair value	$	535		$	52,930		$	—		$	53,465

Related_Party_Transactions_Rel

Related Party Transactions Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2013
Related Party Transaction [Line Items]	'
Schedule of Related Party Accounts Receivable and Payable [Table Text Block]	'
	We have accounts receivable and accounts payable balances related to transactions with other BHC subsidiaries. These balances as of December 31 were as follows (in thousands):
		2013		2012
	Receivable - affiliates	$	4,934	$	5,027
	Accounts payable - affiliates	$	21,082	$	21,896
Schedule of Related Party Notes and Associated Interest Income Expense [Table Text Block]	'
	We had the following balances with the Utility Money Pool as of December 31 (in thousands):
		2013		2012
	Notes receivable (payable), net	$	17,292	$	31,645
Schedule of Related Party Interest Income Expense [Table Text Block]	'
	Net interest income (expense) relating to the Utility Money Pool for the years ended December 31, was as follows (in thousands)
		2013		2012		2011
	Net interest income (expense)	$	505	$	617	$	1,414
Schedule of Revenues and Purchases from Related Parties [Table Text Block]	'
	We had the following related party transactions for the years ended December 31 included in the corresponding captions in the accompanying Statements of Income:
		2013		2012		2011
		(in thousands)
	Revenues:
	Energy sold to Cheyenne Light	$	1,338	$	2,372	$	957
	Rent from electric properties	$	3,627	$	2,661	$	7,523
	Purchases:
	Purchase of coal from WRDC	$	18,542	$	20,690	$	21,319
	Purchase of excess energy from Cheyenne Light	$	3,640	$	3,139	$	4,127
	Purchase of renewable wind energy from Cheyenne Light - Happy Jack	$	1,886	$	1,988	$	1,955
	Purchase of renewable wind energy from Cheyenne Light - Silver Sage	$	3,207	$	3,269	$	3,281
	Corporate support services from Parent, Black Hills Service Company and Black Hills Utility Holdings	$	30,738	$	24,163	$	18,567

Supplemental_Cash_Flows_Inform1

Supplemental Cash Flows Information Supplemental Cash Flows Information (Tables)	12 Months Ended
	Dec. 31, 2013
Supplemental Cash Flow Information [Abstract]	'
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	'
	Years ended December 31,	2013			2012			2011
		(in thousands)
	Non-cash investing and financing activities -
	Property, plant and equipment acquired with accrued liabilities	$	13,590		$	3,969		$	1,882
	Non-cash decrease to money pool note receivable, net	$	(8,000	)	$	(43,984	)	$	—
	Non-cash dividend to Parent company	$	8,000		$	43,984		$	—
	Supplemental disclosure of cash flow information:
	Cash (paid) refunded during the period for -
	Interest (net of amounts capitalized)	$	(19,174	)	$	(17,099	)	$	(16,294	)
	Income taxes	$	219		$	7,176		$	(15,347	)

Commitment_and_Contingencies_C

Commitment and Contingencies Commitment and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Long-term Purchase Commitment [Table Text Block]	'
	Costs incurred under these agreements were as follows for the years ended December 31 (in thousands):
	Contract	Contract Type	2013		2012		2011
	PacifiCorp	Electric capacity and energy	$	13,026	$	13,224	$	12,515
	PacifiCorp	Transmission access	$	1,384	$	1,215	$	1,215
	Thunder Creek	Gas transport capacity	$	633	$	633	$	633
Unrecorded Unconditional Purchase Obligations Disclosure [Table Text Block]	'
	The following is a schedule of future minimum payments required under the power purchase, transmission services, facility and vehicle leases, and gas supply agreements (in thousands):
	2014	$	12,451
	2015	$	12,443
	2016	$	12,443
	2017	$	12,443
	2018	$	6,133
	Thereafter	$	28,764

Quarterly_Historical_Data_Unau1

Quarterly Historical Data (Unaudited) Quarterly Historical Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]	'
Schedule of Quarterly Financial Information [Table Text Block]	'
	The following table sets forth selected unaudited historical operating results data for each quarter (in thousands):
		First		Second		Third		Fourth
		Quarter		Quarter		Quarter		Quarter
	2013
	Operating revenues	$	59,817	$	60,832	$	67,268	$	66,110
	Operating income	$	12,503	$	14,293	$	18,704	$	16,844
	Net income	$	5,582	$	6,652	$	9,298	$	8,641
	2012
	Operating revenues	$	62,270	$	58,372	$	61,134	$	61,533
	Operating income	$	12,742	$	13,859	$	15,361	$	15,619
	Net income	$	6,053	$	6,727	$	8,147	$	6,159

Business_Description_and_Summa

Business Description and Summary of Significant Accounting Policies Regulatory Assets and Liabilities (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Assets	$45,264		$53,242
Regulatory Liabilities	43,518		43,886
Cost Of Removal [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Liabilities Amortization Period	'P53Y		'
Regulatory Liabilities	30,467	[1]	26,630	[1]
Pension Cost [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Liabilities Amortization Period	'P13Y		'
Regulatory Liabilities	10,177	[2]	15,689	[2]
Other Regulatory Liabilities [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Liabilities Amortization Period	'P13Y		'
Regulatory Liabilities	2,874	[3]	1,567	[3]
Loss on Reacquired Debt [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Assets, Amortization Period	'P14Y		'
Regulatory Assets	2,257	[1]	2,501	[1]
Allowance for Cost of Equity Funds Used During Construction [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Assets, Amortization Period	'P45Y		'
Regulatory Assets	8,327	[4]	8,460	[4]
Pension Plan, Defined Benefit [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Assets, Amortization Period	'P13Y		'
Regulatory Assets	15,233	[5]	27,001	[5]
Deferred Fuel Costs [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Assets, Amortization Period	'P1Y		'
Regulatory Assets	7,711	[1]	6,892	[1]
Flow Through Accounting [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Assets, Amortization Period	'P35Y		'
Regulatory Assets	9,723	[1]	8,019	[1]
Other Regulatory Assets [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Assets, Amortization Period	'P2Y		'
Regulatory Assets	2,013	[1]	369	[1]
Rate Case Settlement, Included As Recovery or Reduction to Rate Base With Rate of Return [Member] | Pension Cost [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Liabilities	13,000		'
Rate Case Settlement, Included As Recovery or Reduction to Rate Base With Rate of Return [Member] | Other Regulatory Liabilities [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Liabilities	800		'
Rate Case Settlement, Included As Recovery or Reduction to Rate Base With Rate of Return [Member] | Pension Plan, Defined Benefit [Member]	'		'
Schedule Of Regulatory Assets And Liabilities [Line Items]	'		'
Regulatory Assets	$24,000		'
[1]	Recovery of costs but not allowed a rate of return.
[2]	Approximately $13 million is included in our rate base calculation as a reduction to rate base.
[3]	Approximately $0.8 million is included in our rate base calculation as a reduction to rate base.
[4]	In addition to recovery of costs, we are allowed a rate of return.
[5]	In addition to recovery of costs, we are allowed a return on approximately $24 million according to the approved rate case.

Business_Description_and_Summa1

Business Description and Summary of Significant Accounting Policies Accounts Receivable (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Allowance for Doubtful Accounts Receivable, Current	($220)	($102)
Accounts Receivable, Net, Current	25,799	23,867
Billed Revenues [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	16,300	14,965
Unbilled Revenues [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Accounts Receivable, Gross, Current	$9,719	$9,004

Business_Description_and_Summa2

Business Description and Summary of Significant Accounting Policies Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]	'	'	'
Property, Plant and Equipment, Composite Depreciation Rate for Plants in Service	2.10%	2.20%	2.20%

Property_Plant_and_Equipment_P

Property, Plant and Equipment Property, Plant & Equipment (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Electric Plant, Property, Plant and Equipment, Production	512,444		510,674
Electric Plant, Property, Plant and Equipment, Transmission	115,149		115,092
Electric Plant, Property, Plant and Equipment, Distribution	315,971		304,113
Electric Plant, Property, Plant and Equipment, Plant Acquisition Adjustment	4,870	[1]	4,870	[1]
Electric Plant, Property, Plant and Equipment, General	70,228		71,802
Electric Plant, Property, Plant and Equipment, Plant in Service	1,018,662		1,006,551
Electric Plan, Property, Plant and Equipment, Construction Work in Progress	77,222		18,217
Electric Plant, Property, Plant and Equipment, Gross	1,095,884		1,024,768
Accumulated Depreciation and Amortization, Property, Plant, and Equipment	-334,174		-322,830
Property, Plant and Equipment, Net	761,710		701,938
Acquisition Adjustment, Remaining Amortization Period	'17 years		'
Electric Production [Member] | Weighted average useful life [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'51 years		'51 years
Electric Production [Member] | Minimum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'45 years		'
Electric Production [Member] | Maximum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'65 years		'
Electric Transmission [Member] | Weighted average useful life [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'46 years		'46 years
Electric Transmission [Member] | Minimum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'40 years		'
Electric Transmission [Member] | Maximum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'60 years		'
Electric Distribution [Member] | Weighted average useful life [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'39 years		'38 years
Electric Distribution [Member] | Minimum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'16 years		'
Electric Distribution [Member] | Maximum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'45 years		'
Plant Acquisition Adjustment [Member] | Weighted average useful life [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'32 years	[1]	'32 years
Plant Acquisition Adjustment [Member] | Minimum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'32 years		'
Plant Acquisition Adjustment [Member] | Maximum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'32 years		'
General [Member] | Weighted average useful life [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'22 years		'22 years
General [Member] | Minimum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'8 years		'
General [Member] | Maximum years [Member]	'		'
Public Utilities, Property, Plant and Equipment, Net [Abstract]	'		'
Property, Plant and Equipment, Useful Life (Years)	'45 years		'
[1]	The plant acquisition adjustment is included in rate base and is being recovered with 17 years remaining.

Jointly_Owned_Facilities_Joint

Jointly Owned Facilities Jointly Owned Facilities (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Wyodak Plant [Member]	'
Jointly Owned Utility Plant Interests [Line Items]	'
Jointly Owned Utility Plant, Proportionate Ownership Percentage	20.00%
Jointly Owned Utility Plant, Plant in Service	$109,800
Jointly Owned Utility Plant, Construction Work in Progress	192
Jointly Owned Utility Plant, Accumulated Depreciation	50,595
Transmission Tie [Member]	'
Jointly Owned Utility Plant Interests [Line Items]	'
Jointly Owned Utility Plant, Proportionate Ownership Percentage	35.00%
Jointly Owned Utility Plant, Plant in Service	19,648
Jointly Owned Utility Plant, Construction Work in Progress	0
Jointly Owned Utility Plant, Accumulated Depreciation	4,741
Wygen I I I Generating Facility [Member]	'
Jointly Owned Utility Plant Interests [Line Items]	'
Jointly Owned Utility Plant, Proportionate Ownership Percentage	52.00%
Jointly Owned Utility Plant, Plant in Service	131,468
Jointly Owned Utility Plant, Construction Work in Progress	713
Jointly Owned Utility Plant, Accumulated Depreciation	$10,593

LongTerm_Debt_Long_Term_Debt_D

Long-Term Debt Long Term Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Debt Instrument [Line Items]	'		'		'
Long-term Debt	$269,948,000		$269,944,000		'
Deferred Finance Costs [Abstract]	'		'		'
Deferred Finance Costs, Noncurrent, Net	2,800,000		2,900,000		'
Amortization of Financing Costs	100,000		200,000		500,000
First Mortgage Bonds Due 2032 [Member]	'		'		'
Debt Instrument [Line Items]	'		'		'
Debt Instrument, Maturity Date	15-Aug-32		'		'
Debt Instrument, Interest Rate, Stated Percentage	7.23%		'		'
Long-term Debt, Gross	75,000,000		75,000,000		'
First Mortgage Bonds Due 2039 [Member]	'		'		'
Debt Instrument [Line Items]	'		'		'
Debt Instrument, Maturity Date	1-Nov-39		'		'
Debt Instrument, Interest Rate, Stated Percentage	6.13%		'		'
Long-term Debt, Gross	180,000,000		180,000,000		'
Debt Instrument, Unamortized Discount	-107,000		-111,000		'
Polution Control Revenue Bonds Due 2024 [Member]	'		'		'
Debt Instrument [Line Items]	'		'		'
Debt Instrument, Maturity Date	1-Oct-24		'		'
Debt Instrument, Interest Rate, Stated Percentage	5.35%		'		'
Long-term Debt, Gross	12,200,000		12,200,000		'
Bonds Due 2024 [Member]	'		'		'
Debt Instrument [Line Items]	'		'		'
Debt Instrument, Maturity Date	1-Jun-24		'		'
Long-term Debt, Variable Interest, Percentage Rate	0.75%	[1]	'		'
Long-term Debt, Gross	$2,855,000	[1]	$2,855,000	[1]	'
[1]	Variable interest rate at December 31, 2013.

LongTerm_Debt_Schedule_of_Matu

Long-Term Debt Schedule of Maturities of Long-term Debt (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Debt Instrument [Line Items]	'
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal after Year Five	$270,055

Fair_Value_of_Financial_Instru1

Fair Value of Financial Instruments Fair Value of Financial Instruments (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'	'
Cash and Cash Equivalents, at Carrying Value	$2,259		$3,805		$2,812	$2,045
Long-term debt, including current maturities, at carrying value	269,948		269,944		'	'
Carrying Amount	'		'		'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'	'
Cash and Cash Equivalents, at Carrying Value	2,259	[1]	3,805	[1]	'	'
Long-term debt, including current maturities, at carrying value	269,948	[2]	269,944	[2]	'	'
Fair Value	'		'		'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'		'	'
Cash and Cash Equivalents, Fair Value Disclosure	2,259	[1]	3,805	[1]	'	'
Long-term debt including current maturities, at fair value	$317,531	[2]	$359,567	[2]	'	'
[1]	Fair value approximates carrying value due to either short-term length of maturity or variable interest rates that approximate prevailing market rates and therefore is classified in Level 1 in the fair value hierarchy.
[2]	Long-term debt is valued using the market approach based on observable inputs of quoted market prices and yields available for debt instruments either directly or indirectly for similar maturities and debt ratings in active markets and therefore is classified in Level 2 in the fair value hierarchy. The carrying amount of our variable rate debt approximates fair value due to the variable interest rates with short reset periods. For additional information on our long-term debt, see Note 4 to the Financial Statements.

Income_Taxes_Current_and_Defer

Income Taxes Current and Deferred Income Tax Expense (Benefit) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Expense Benefit [Line Items]	'	'	'
Current Income Tax Expense (Benefit)	($163)	($10,319)	$14,921
Deferred Income Tax Expense (Benefit)	13,582	24,628	-2,931
Income Tax Expense (Benefit)	$13,419	$14,309	$11,990

Income_Taxes_Deferred_Income_T

Income Taxes Deferred Income Tax Assets and Liabilities (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Components of Deferred Tax Assets [Abstract]	'	'
Deferred Tax Assets, Employee Benefits	$4,567	$5,094
Deferred Tax Assets, Net Operating Loss	4,197	10,441
Deferred Tax Assets,Regulatory Liabilities	6,398	13,433
Deferred Tax Assets, Other	2,193	2,381
Total Deferred Tax Assets	17,355	31,349
Components of Deferred Tax Liabilities [Abstract]	'	'
Deferred Tax Liabilities, Accelerated Depreciation and Other Plant Related Differenes	-161,990	-154,989
Deferred Tax Liabilities, Allowance for Funds Used During Construction	-8,190	-5,499
Deferred Tax Liabilities, Regulatory Assets	-3,540	-5,767
Deferred Tax Liability, Employee Benefits	3,467	3,610
Deferred Tax Liabilities, Deferred Costs	-4,240	-2,608
Deferred Tax Liabilities Other	-1,067	-1,163
Total Deferred Tax Liabilities	-182,494	-173,636
Deferred Tax Assets (Liabilities), Net	($165,139)	($142,287)

Income_Taxes_Effective_Tax_Rat

Income Taxes Effective Tax Rate Differences from Statutory Tax Rates (Details)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Effective Tax Rate Reconciliation [Line Items]	'		'		'
Effective Income Tax Rate Reconciliation, Federal Statutory Rate	35.00%		35.00%		35.00%
Effective Income Tax Rate Reconciliation, Amortization of excess deferred and investment tax credits	-0.30%		-0.30%		-0.40%
Effective Income Tax Rate Reconciliation, Allowance For Other Funds Used During Construction, Equity	0.00%		-0.10%		-0.60%
Effective Income Tax Rate Reconciliation, Flow Through Accounting	-2.50%	[1]	-3.50%	[1]	-3.40%	[1]
Effective Income Tax Rate Reconciliation, Prior Year Deferred Adjustment	0.00%		3.60%	[2]	0.00%
Effective Income Tax Rate Reconciliation, Tax Credit	-0.80%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments	-0.60%		-0.10%		0.10%
Effective Income Tax Rate	30.80%		34.60%		30.70%
[1]	The flow-through adjustments relate primarily to an accounting method change for tax purposes that allows us to take a current tax deduction for repair costs that continue to be capitalized for book purposes. We recorded a deferred income tax liability in recognition of the temporary difference created between book and tax treatment and we flowed the tax benefit through to our customers in the form of lower rates as a result of a rate case settlement that occurred during 2010. A regulatory asset was established to reflect the recovery of future increases in taxes payable from customers as the temporary differences reverse. As a result of this regulatory treatment, we continue to record a tax benefit consistent with the flow through method.
[2]	The adjustment was a non-recurring unfavorable true-up attributable to property related deferred income taxes. The removal of the impact of such an adjustment is more appropriately reflective of the effective rate on a recurring basis.

Income_Taxes_Reconciliation_of

Income Taxes Reconciliation of unrecognized tax benefits (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'
Liability for Uncertain Tax Positions, Noncurrent, Beginning of Period	$2,078,000	$3,595,000
Unrecognized Tax Benefits, Reductions for Prior Year Tax Positions	-155,000	-1,586,000
Unrecognized Tax Benefits, Additions for Current Year Tax Positions	520,000	69,000
Liability for Uncertain Tax Positions, Noncurrent, End of Period	2,443,000	2,078,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$500,000	'

Income_Taxes_Net_Operating_Los

Income Taxes Net Operating Loss Carryforwards (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]	'
Operating Loss Carryforwards, Expiration Date	31-Dec-31
Internal Revenue Service (IRS) [Member]	'
Operating Loss Carryforwards [Line Items]	'
Operating Loss Carryforwards	14

Comprehensive_Income_Other_Com

Comprehensive Income Other Comprehensive income (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Interest Costs Incurred	'	'	'	'	'	'	'	'	$19,725,000	$17,602,000	$16,712,000
Income tax expense	'	'	'	'	'	'	'	'	-13,419,000	-14,309,000	-11,990,000
Net income	8,641,000	9,298,000	6,652,000	5,582,000	6,159,000	8,147,000	6,727,000	6,053,000	30,173,000	27,086,000	27,097,000
Interest Rate Swaps, Interest Expense, Cash Flow Hedges [Member] | Interest Rate Contract [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'	'	'	'	'	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Interest Costs Incurred	'	'	'	'	'	'	'	'	64,000	64,000	'
Income tax expense	'	'	'	'	'	'	'	'	-23,000	-23,000	'
Net income	'	'	'	'	'	'	'	'	41,000	41,000	'
Amortization of Defined Benefit Plans, Actuarial Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'	'	'	'	'	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Utilities Operating Expense, Maintenance, Operations, and Other Costs and Expenses	'	'	'	'	'	'	'	'	66,000	0	'
Amortization of Defined Benefit Plans [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]	'	'	'	'	'	'	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Income tax expense	'	'	'	'	'	'	'	'	-23,000	0	'
Net income	'	'	'	'	'	'	'	'	43,000	0	'
First Mortgage Bonds Due 2032 [Member]	'	'	'	'	'	'	'	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Derivative, Notional Amount	50,000,000	'	'	'	'	'	'	'	50,000,000	'	'
Debt Instrument, Maturity Date	'	'	'	'	'	'	'	'	15-Aug-32	'	'
Derivative, Maturity Date	'	'	'	'	'	'	'	'	8-Aug-02	'	'
Realized Loss Included Accumulated Other Comprehensive Income (Loss)	$1,800,000	'	'	'	'	'	'	'	$1,800,000	'	'

Comprehensive_Income_Accumulat

Comprehensive Income Accumulated Other Comprehensive Income (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax	($1,420)	($1,290)	'
Other comprehensive income (loss)	223	-130	-28
Accumulated Other Comprehensive Income (Loss), Net of Tax	-1,197	-1,420	-1,290
Employee Benefit Plans, AOCI [Member]	'	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-660	-489	'
Other comprehensive income (loss)	182	-171	'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-478	-660	'
Interest Rate Swap [Member] | Interest Rate Swaps, Cash Flow Hedges, AOCI [Member]	'	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'
Accumulated Other Comprehensive Income (Loss), Net of Tax	-760	-801	'
Other comprehensive income (loss)	41	41	'
Accumulated Other Comprehensive Income (Loss), Net of Tax	($719)	($760)	'

Employee_Benefit_Plans_Narrati

Employee Benefit Plans Narrative (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'		'		'
Defined Benefit Plan, Measurement Date	'December 31		'		'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.25%		7.25%		'
Pension Plan, Defined Benefit [Member]	'		'		'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'		'		'
Defined Benefit Plan, Unfunded Status of Plan	$3.80		'		'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.25%	[1]	7.25%	[1]	7.75%	[1]
Other Postretirement Benefit Plans, Defined Benefit [Member]	'		'		'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'		'		'
Defined Benefit Plan, Unfunded Status of Plan	5.9		'		'
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'		'		'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'		'		'
Defined Benefit Plan, Unfunded Status of Plan	$3.10		'		'
[1]	*The expected rate of return on plan assets is 6.75% for the calculation of the 2014 net periodic pension cost.

Employee_Benefit_Plans_Target_

Employee Benefit Plans Target Plan Assets Allocation (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Target Plan Asset Allocations	100.00%	100.00%
Equity Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Target Plan Asset Allocations	26.00%	51.00%
Real Estate [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Target Plan Asset Allocations	4.00%	0.00%
Fixed Income Funds [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Target Plan Asset Allocations	58.00%	48.00%
Cash and Cash Equivalents [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Target Plan Asset Allocations	1.00%	1.00%
Hedge Funds [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Defined Benefit Plan, Target Plan Asset Allocations	11.00%	0.00%

Employee_Benefit_Plans_Plan_Co

Employee Benefit Plans Plan Contribution (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	$0	'
Defined Contribution Plan, Company Retirement [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Defined Contribution Plans, Contributions by Employer	421,000	404,000
Defined Contribution Plan, 401K [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Defined Contribution Plans, Contributions by Employer	1,301,000	1,328,000
Pension Plan, Defined Benefit [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Defined Benefit Plan, Contributions by Employer	2,299,000	6,835,000
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Defined Benefit Plan, Contributions by Employer	0	0
Pension and Other Postretirement Benefit Contributions	578,000	835,000
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Defined Benefit Plan, Contributions by Employer	0	0
Pension and Other Postretirement Benefit Contributions	$217,000	$256,000

Employee_Benefit_Plans_Employe1

Employee Benefit Plans Employee Benefit Plans Fair Value Measurements (Details) (Pension Plan, Defined Benefit [Member], USD $)	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	$56,405		$53,465	$45,017
Fixed Income Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	213		'	'
Common Collective Trust, Cash and Cash Equivalents [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	252		'	'
Common Collective Trust, Equity [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	14,833		27,267	'
Common Collective Trust, Fixed Income [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	32,742		21,127	'
Real Estate Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	2,400		'	'
Hedge Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	5,965		'	'
Cash and Cash Equivalents [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		535	'
Structured Products [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		4,536	'
Fair Value, Level 1 [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		535	'
Fair Value, Level 1 [Member] | Fixed Income Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		'	'
Fair Value, Level 1 [Member] | Common Collective Trust, Cash and Cash Equivalents [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		'	'
Fair Value, Level 1 [Member] | Common Collective Trust, Equity [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		0	'
Fair Value, Level 1 [Member] | Common Collective Trust, Fixed Income [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		0	'
Fair Value, Level 1 [Member] | Real Estate Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		'	'
Fair Value, Level 1 [Member] | Hedge Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		'	'
Fair Value, Level 1 [Member] | Cash and Cash Equivalents [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		535	'
Fair Value, Level 1 [Member] | Structured Products [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		0	'
Fair Value, Level 2 [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	48,722		52,930	'
Fair Value, Level 2 [Member] | Fixed Income Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	213		'	'
Fair Value, Level 2 [Member] | Common Collective Trust, Cash and Cash Equivalents [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	252		'	'
Fair Value, Level 2 [Member] | Common Collective Trust, Equity [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	14,833		27,267	'
Fair Value, Level 2 [Member] | Common Collective Trust, Fixed Income [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	32,742		21,127	'
Fair Value, Level 2 [Member] | Real Estate Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	682		'	'
Fair Value, Level 2 [Member] | Hedge Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		0	'
Fair Value, Level 2 [Member] | Cash and Cash Equivalents [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		0	'
Fair Value, Level 2 [Member] | Structured Products [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		4,536	'
Fair Value, Level 3 [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	7,683		0	'
Fair Value, Level 3 [Member] | Fixed Income Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		'	'
Fair Value, Level 3 [Member] | Common Collective Trust, Cash and Cash Equivalents [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		'	'
Fair Value, Level 3 [Member] | Common Collective Trust, Equity [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		0	'
Fair Value, Level 3 [Member] | Common Collective Trust, Fixed Income [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	0		0	'
Fair Value, Level 3 [Member] | Real Estate Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	1,718	[1]	'	'
Fair Value, Level 3 [Member] | Hedge Funds [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	5,965	[2]	'	'
Fair Value, Level 3 [Member] | Cash and Cash Equivalents [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		0	'
Fair Value, Level 3 [Member] | Structured Products [Member]	'		'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'		'	'
Defined Benefit Plan, Fair Value of Plan Assets	'		$0	'
[1]	The underlying net asset value in the Common Collective Trust - Real Estate fund is determined by appraisal of the properties held in the Trust. As part of the Trustee's valuation process, properties are externally appraised generally on an annual basis. The appraisals are conducted by reputable independent appraisal firms and signed by appraisers that are members of the Appraisal Institute, with the professional designation of Member, Appraisal Institute. All external appraisals are performed in accordance with the Uniform Standards of Professional Appraisal Practices. We receive monthly statements from the Trustee along with the annual schedule of investments and rely on these reports for pricing the units of the fund. The fund does contain a participant withdrawal policy.
[2]	The fair value of Level 3 is determined based on pricing provided or reviewed by third-party administrator to our investment managers. While the input amounts used by the pricing vendor in determining fair value are not provided, and therefore, unavailable for our review, the asset results are reviewed and monitored to ensure the fair values are reasonable and in line with market experience in similar asset classes. Additionally, the audited financial statements of the funds will be reviewed at the time they are issued.

Employee_Benefit_Plans_Level_3

Employee Benefit Plans Level 3 Roll Forward (Details) (Pension Plan, Defined Benefit [Member], USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2013		Dec. 31, 2013	Dec. 31, 2013
In Thousands, unless otherwise specified				Fair Value, Level 3 [Member]	Fair Value, Level 3 [Member]	Real Estate Funds [Member]	Real Estate Funds [Member]		Hedge Funds [Member]	Hedge Funds [Member]
							Fair Value, Level 3 [Member]			Fair Value, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'	'	'	'	'	'		'	'
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	'	'	'	'	'	'	$0		'	'
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	'	'	'	'	'	'	1,550		'	'
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	'	'	'	'	'	'	5,834		'	'
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Unrealized Gain (Loss)	'	'	'	'	'	'	317		'	'
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Realized Gain (Loss)	'	'	'	'	'	'	-3		'	'
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	'	'	'	'	'	'	-15		'	'
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	'	'	'	'	'	'	7,683		'	'
Defined Benefit Plan, Fair Value of Plan Assets, Level 3 Assets	$56,405	$53,465	$45,017	$7,683	$0	$2,400	$1,718	[1]	$5,965	$5,965	[2]
[1]	The underlying net asset value in the Common Collective Trust - Real Estate fund is determined by appraisal of the properties held in the Trust. As part of the Trustee's valuation process, properties are externally appraised generally on an annual basis. The appraisals are conducted by reputable independent appraisal firms and signed by appraisers that are members of the Appraisal Institute, with the professional designation of Member, Appraisal Institute. All external appraisals are performed in accordance with the Uniform Standards of Professional Appraisal Practices. We receive monthly statements from the Trustee along with the annual schedule of investments and rely on these reports for pricing the units of the fund. The fund does contain a participant withdrawal policy.
[2]	The fair value of Level 3 is determined based on pricing provided or reviewed by third-party administrator to our investment managers. While the input amounts used by the pricing vendor in determining fair value are not provided, and therefore, unavailable for our review, the asset results are reviewed and monitored to ensure the fair values are reasonable and in line with market experience in similar asset classes. Additionally, the audited financial statements of the funds will be reviewed at the time they are issued.

Employee_Benefit_Plans_Changes

Employee Benefit Plans Changes in Benefit Obligations (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Pension Plan, Defined Benefit [Member]	'		'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'		'	'
Defined Benefit Plan, Projected Benefit Obligation, Period Start	$69,820		$65,557	'
Defined Benefit Plan, Service Cost	852		765	798
Defined Benefit Plan, Interest Cost	2,969		2,969	3,092
Defined Benefit Plan, Actuarial (Gain) Loss	-7,818		4,510	'
Defined Benefit Plan, Plan Amendments	0		0	'
Defined Benefit Plan, Benefits Paid	-4,850		-2,850	'
Defined Benefit Plan, Asset Transfer (to) from Affiliate	-750		-1,131	'
Defined Benefit Plan, Curtailments	0		0	'
Defined Benefit Plan, Medicare Part D Adjustments	0		0	'
Defined Benefit Plan, Contributions by Plan Participants	0		0	'
Defined Benefit Plan, Projected Benefit Obligation, Period End	60,223		69,820	65,557
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'		'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'		'	'
Defined Benefit Plan, Projected Benefit Obligation, Period Start	3,427		2,292	'
Defined Benefit Plan, Service Cost	0		0	0
Defined Benefit Plan, Interest Cost	133		104	114
Defined Benefit Plan, Actuarial (Gain) Loss	-212		1,287	'
Defined Benefit Plan, Plan Amendments	0		0	'
Defined Benefit Plan, Benefits Paid	0		0	'
Defined Benefit Plan Benefits Paid from Company Assets	-217		-256	'
Defined Benefit Plan, Asset Transfer (to) from Affiliate	0		0	'
Defined Benefit Plan, Curtailments	0		0	'
Defined Benefit Plan, Medicare Part D Adjustments	0		0	'
Defined Benefit Plan, Contributions by Plan Participants	0		0	'
Defined Benefit Plan, Projected Benefit Obligation, Period End	3,131		3,427	2,292
Other Postretirement Benefit Plans, Defined Benefit [Member]	'		'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'		'	'
Defined Benefit Plan, Projected Benefit Obligation, Period Start	6,766		8,207	'
Defined Benefit Plan, Service Cost	216		214	210
Defined Benefit Plan, Interest Cost	239		343	365
Defined Benefit Plan, Actuarial (Gain) Loss	-459		-1,748	'
Defined Benefit Plan, Plan Amendments	-342	[1]	0	'
Defined Benefit Plan, Benefits Paid	0		0	'
Defined Benefit Plan Benefits Paid From Plan and Company Assets	-1,045		-835	'
Defined Benefit Plan, Asset Transfer (to) from Affiliate	-75		26	'
Defined Benefit Plan, Curtailments	0		0	'
Defined Benefit Plan, Medicare Part D Adjustments	82		71	'
Defined Benefit Plan, Contributions by Plan Participants	468		488	'
Defined Benefit Plan, Projected Benefit Obligation, Period End	$5,850		$6,766	$8,207
[1]	Reflects Board of Directors approval of increase to Companybs contribution to RMSA account.

Employee_Benefit_Plans_Changes1

Employee Benefit Plans Changes in Plan Assets (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Pension Plan, Defined Benefit [Member]	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'
Defined Benefit Plan, Market Value of Plan Assets, Beginning of Period	$53,465	$45,017
Defined Benefit Plan, Investment Income	6,070	5,240
Defined Benefit Plan, Benefits Paid	-4,850	-2,850
Defined Benefit Plan, Contributions by Employer	2,299	6,835
Defined Benefit Plan, Asset Transfer (to) from Affiliate	-579	-777
Defined Benefit Plan, Market Value of Plan Assets, End of Period	56,405	53,465
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'
Defined Benefit Plan, Market Value of Plan Assets, Beginning of Period	0	0
Defined Benefit Plan, Investment Income	0	0
Defined Benefit Plan, Benefits Paid	0	0
Defined Benefit Plan, Contributions by Employer	0	0
Defined Benefit Plan, Asset Transfer (to) from Affiliate	0	0
Defined Benefit Plan, Market Value of Plan Assets, End of Period	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'
Defined Benefit Plan, Market Value of Plan Assets, Beginning of Period	0	0
Defined Benefit Plan, Investment Income	0	0
Defined Benefit Plan, Benefits Paid	0	0
Defined Benefit Plan, Contributions by Employer	0	0
Defined Benefit Plan, Asset Transfer (to) from Affiliate	0	0
Defined Benefit Plan, Market Value of Plan Assets, End of Period	$0	$0

Employee_Benefit_Plans_Amounts

Employee Benefit Plans Amounts Recognized in the Balance Sheet (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Regulatory Assets, Defined Benefit Plans	$45,264	$53,242
Regulatory Liabilities, Defined Benefit Plans	-43,518	-43,886
Non-Current Liabilities, Defined Benefit Plans	-12,105	-25,888
Pension Plan, Defined Benefit [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Regulatory Assets, Defined Benefit Plans	13,735	26,683
Current Liabilities, Defined Benefit Plans	0	0
Non-Current Liabilities, Defined Benefit Plans	-3,818	-16,356
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Regulatory Assets, Defined Benefit Plans	0	0
Current Liabilities, Defined Benefit Plans	-216	-216
Non-Current Liabilities, Defined Benefit Plans	-2,915	-3,211
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'
Regulatory Assets, Defined Benefit Plans	2,781	'
Regulatory Liabilities, Defined Benefit Plans	'	-2,174
Current Liabilities, Defined Benefit Plans	-491	-438
Non-Current Liabilities, Defined Benefit Plans	($5,372)	($6,321)

Employee_Benefit_Plans_Accumul

Employee Benefit Plans Accumulated Benefit Obligation (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Pension Plan, Defined Benefit [Member]	'		'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'		'	'
Defined Benefit Plan, Service Cost	$852		$765	$798
Defined Benefit Plan, Accumulated Benefit Obligation	55,283		63,417	'
Defined Benefit Plan, Interest Cost	2,969		2,969	3,092
Defined Benefit Plan, Actuarial Gain (Loss)	-7,818		4,510	'
Defined Benefit Plan, Plan Amendments	0		0	'
Defined Benefit Plan, Benefits Paid	4,850		2,850	'
Defined Benefit Plan, Benefit Obligation Transfer	750		1,131	'
Defined Benefit Plan, Curtailments	0		0	'
Defined Benefit Plan, Medicare Part D Adjustments	0		0	'
Defined Benefit Plan, Contributions by Plan Participants	0		0	'
Defined Benefit Plan, Benefit Obligation	60,223		69,820	65,557
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'		'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'		'	'
Defined Benefit Plan, Service Cost	0		0	0
Defined Benefit Plan, Accumulated Benefit Obligation	3,131		3,427	'
Defined Benefit Plan, Interest Cost	133		104	114
Defined Benefit Plan, Actuarial Gain (Loss)	-212		1,287	'
Defined Benefit Plan, Plan Amendments	0		0	'
Defined Benefit Plan, Benefits Paid	0		0	'
Defined Benefit Plan Benefits Paid from Company Assets	217		256	'
Defined Benefit Plan, Benefit Obligation Transfer	0		0	'
Defined Benefit Plan, Curtailments	0		0	'
Defined Benefit Plan, Medicare Part D Adjustments	0		0	'
Defined Benefit Plan, Contributions by Plan Participants	0		0	'
Defined Benefit Plan, Benefit Obligation	3,131		3,427	2,292
Other Postretirement Benefit Plans, Defined Benefit [Member]	'		'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'		'	'
Defined Benefit Plan, Service Cost	216		214	210
Defined Benefit Plan, Accumulated Benefit Obligation	5,850		6,766	'
Defined Benefit Plan, Interest Cost	239		343	365
Defined Benefit Plan, Actuarial Gain (Loss)	-459		-1,748	'
Defined Benefit Plan, Plan Amendments	-342	[1]	0	'
Defined Benefit Plan, Benefits Paid	0		0	'
Defined Benefit Plan Benefits Paid From Plan and Company Assets	1,045		835	'
Defined Benefit Plan, Benefit Obligation Transfer	75		-26	'
Defined Benefit Plan, Curtailments	0		0	'
Defined Benefit Plan, Medicare Part D Adjustments	82		71	'
Defined Benefit Plan, Contributions by Plan Participants	468		488	'
Defined Benefit Plan, Benefit Obligation	$5,850		$6,766	$8,207
[1]	Reflects Board of Directors approval of increase to Companybs contribution to RMSA account.

Employee_Benefit_Plans_Compone

Employee Benefit Plans Components of Net Periodic Expense (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plan, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Defined Benefit Plan, Service Cost, Net Periodic Expense	$852	$765	$798
Defined Benefit Plan, Interest Cost, Net Periodic Expense	2,969	2,969	3,092
Defined Benefit Plan, Expected Return on Plan Assets, Net Periodic Expense	-3,764	-3,139	-3,619
Defined Benefit Plan, Amortization of Prior Service Cost (Credit), Net Periodic Expense	43	57	62
Defined Benefit Plan, Amortization of Transition Obligations (Assets), Net Periodic Expense	2,609	0	0
Defined Benefit Plan, Recognition of Net Actuarial Loss (Gain), Net Periodic Expense	0	2,599	1,486
Defined Benefit Plan, Curtailment Expense, Net Periodic Expense	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	2,709	3,251	1,819
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Defined Benefit Plan, Service Cost, Net Periodic Expense	0	0	0
Defined Benefit Plan, Interest Cost, Net Periodic Expense	133	104	114
Defined Benefit Plan, Expected Return on Plan Assets, Net Periodic Expense	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit), Net Periodic Expense	0	0	0
Defined Benefit Plan, Amortization of Transition Obligations (Assets), Net Periodic Expense	0	0	0
Defined Benefit Plan, Recognition of Net Actuarial Loss (Gain), Net Periodic Expense	66	55	48
Defined Benefit Plan, Curtailment Expense, Net Periodic Expense	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	199	159	162
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Defined Benefit Plan, Service Cost, Net Periodic Expense	216	214	210
Defined Benefit Plan, Interest Cost, Net Periodic Expense	239	343	365
Defined Benefit Plan, Expected Return on Plan Assets, Net Periodic Expense	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit), Net Periodic Expense	-278	-278	-314
Defined Benefit Plan, Amortization of Transition Obligations (Assets), Net Periodic Expense	0	0	0
Defined Benefit Plan, Recognition of Net Actuarial Loss (Gain), Net Periodic Expense	9	139	163
Defined Benefit Plan, Curtailment Expense, Net Periodic Expense	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	$186	$418	$424

Employee_Benefit_Plans_Accumul1

Employee Benefit Plans Accumulated Other Comprehensive Income (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Pension Plan, Defined Benefit [Member]	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]	'	'
Defined Benefit Plan, Accumulated Other Comprehensive Income Income (Loss), after Tax	$0	$0
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Prior Service (Cost) Credit, after Tax	0	0
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	0	0
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]	'	'
Defined Benefit Plan, Amortization of Net Gains (Losses)	611	'
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	28	'
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year	639	'
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]	'	'
Defined Benefit Plan, Accumulated Other Comprehensive Income Income (Loss), after Tax	-479	-660
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Prior Service (Cost) Credit, after Tax	0	0
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	-479	-660
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]	'	'
Defined Benefit Plan, Amortization of Net Gains (Losses)	29	'
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0	'
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year	29	'
Other Postretirement Benefit Plans, Defined Benefit [Member]	'	'
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]	'	'
Defined Benefit Plan, Accumulated Other Comprehensive Income Income (Loss), after Tax	0	0
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Prior Service (Cost) Credit, after Tax	0	0
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	0	0
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]	'	'
Defined Benefit Plan, Amortization of Net Gains (Losses)	0	'
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	-206	'
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year	($206)	'

Employee_Benefit_Plans_Defined

Employee Benefit Plans Defined Benefit Plans Assumptions (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]	'		'		'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted Average Expected Long-term Return on Assets	7.25%		7.25%		'
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]	'		'		'
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components	9		'		'
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	179		'		'
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components	-9		'		'
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	-165		'		'
Pension Plan, Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]	'		'		'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted Average Discount Rate	5.10%		4.35%		4.65%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted Average Rate of Compensation Levels	3.86%		3.91%		3.67%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]	'		'		'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighed Average Discount Rate	4.35%		4.65%		5.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted Average Expected Long-term Return on Assets	7.25%	[1]	7.25%	[1]	7.75%	[1]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted Average Rate of Compensation Levels	3.91%		3.67%		3.70%
Defined Benefit Plan Assumptions Used In Calculating Net Periodic Benefit Cost Expected Rate of Return On Assets For Next Fiscal Year	6.75%		'		'
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]	'		'		'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted Average Discount Rate	4.68%		4.25%		4.70%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]	'		'		'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighed Average Discount Rate	3.88%		4.70%		5.00%
Other Postretirement Benefit Plans, Defined Benefit [Member]	'		'		'
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]	'		'		'
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted Average Discount Rate	4.45%		3.65%		4.35%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]	'		'		'
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighed Average Discount Rate	3.65%		4.35%		5.00%
Age, Lower Than Retirement [Member]	'		'		'
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]	'		'		'
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	7.50%		7.75%		'
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.50%		4.50%		'
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate	'2027		'		'
Age, Greater Than Retirement [Member]	'		'		'
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]	'		'		'
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	6.25%		6.50%		'
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.50%		4.50%		'
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate	'2026		'		'
[1]	*The expected rate of return on plan assets is 6.75% for the calculation of the 2014 net periodic pension cost.

Employee_Benefit_Plans_Project

Employee Benefit Plans Projected Benefit Plan Payments (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Pension Plan, Defined Benefit [Member]	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$3,177
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	3,227
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	3,270
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	3,367
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	3,483
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	20,002
Supplemental Employee Retirement Plans, Defined Benefit [Member]	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	217
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	214
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	184
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	213
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	210
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	1,271
Other Postretirement Benefit Plans, Defined Benefit [Member]	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	491
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	432
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	410
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	418
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	473
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	$2,483

Employee_Benefit_Plans_Defined1

Employee Benefit Plans Defined Contribution Plan (Details)	12 Months Ended
	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	50.00%
Defined Contribution Plan, Employee Vesting Period	'5 years
Not Full Vested [Member]	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	20.00%

Related_Party_Transactions_Rel1

Related Party Transactions Related Party Transactions (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Related Party Transaction [Line Items]	'	'	'
Receivables - affiliates	$4,934	$5,027	'
Accounts payable - affiliates	21,082	21,896	'
Related Party Transaction, Utility Money Pool Interest Rate	1.60%	'	'
Notes Receivable (Payable), net, Utility Money Pool	17,292	31,645	'
Interest Income (Expense), Related Party	505	617	1,414
Parent [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Non-cash Dividend to Parent Company	8,000	43,984	0
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	1.00%	'	'
Subsidiary of Common Parent [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Transfer from Investments	8,000	43,984	0
Coal, Purchased [Member] | Subsidiary of Common Parent [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Costs and Expenses, Related Party	18,542	20,690	21,319
Purchase of Excess Energy, Cheyenne Light [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Costs and Expenses, Related Party	3,640	3,139	4,127
Happy Jack Wind Purchase Power Agreeement [Member] | Subsidiary of Common Parent [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	3-Sep-28	'	'
Number of Megawatts Capacity Purchased Under Long-term Contract	15	'	'
Costs and Expenses, Related Party	1,886	1,988	1,955
Silver Sage Wind Power Purchase Agreement [Member] | Subsidiary of Common Parent [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	30-Sep-29	'	'
Number of Megawatts Capacity Purchased Under Long-term Contract	20	'	'
Cost of Purchased Power, Related Party	3,207	3,269	3,281
Allocated Costs From Related Parties [Member] | Subsidiary of Common Parent [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Costs and Expenses, Related Party	30,738	24,163	18,567
Energy sold to Cheyenne Light [Member] | Subsidiary of Common Parent [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Revenue from Related Parties	1,338	2,372	957
Lease Agreements [Member] | Subsidiary of Common Parent [Member]	'	'	'
Related Party Transaction [Line Items]	'	'	'
Revenue from Related Parties	$3,627	$2,661	$7,523

Supplemental_Cash_Flows_Inform2

Supplemental Cash Flows Information Supplemental Cash Flows Information (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]	'	'	'
Property, Plant and Equipment Acquired with Accrued Liabilities	$13,590	$3,969	$1,882
Interest and Income Taxes Paid Refunded, Cash Flow Information [Abstract]	'	'	'
Interest (paid) refunded, (net of amounts capitalized)	-19,174	-17,099	-16,294
Income taxes (paid) refunded, net	219	7,176	-15,347
Subsidiary of Common Parent [Member]	'	'	'
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]	'	'	'
Non-cash Payment of Notes Receivable, Related Parties	-8,000	-43,984	0
Parent [Member]	'	'	'
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]	'	'	'
Non-cash Dividend to Parent Company	$8,000	$43,984	$0

Commitment_and_Contingencies_C1

Commitment and Contingencies Commitment and Contingencies (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Long-term Debt, Fiscal Year Maturity [Abstract]	'	'	'
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	$12,451	'	'
Unrecorded Unconditional Purchase Obligation, Due within Two Years	12,443	'	'
Unrecorded Unconditional Purchase Obligation, Due within Three Years	12,443	'	'
Unrecorded Unconditional Purchase Obligation, Due within Four Years	12,443	'	'
Unrecorded Unconditional Purchase Obligation, Due within Five Years	6,133	'	'
Unrecorded Unconditional Purchase Obligation, Due after Five Years	28,764	'	'
M D U, Montana Dakota Utilities [Member]	'	'	'
Sales Capacity Commitments [Abstract]	'	'	'
Number of MW Sold Under Long-Term Contract	25	'	'
City Of Gillette [Member]	'	'	'
Sales Capacity Commitments [Abstract]	'	'	'
Number of MW Sold Under Long-Term Contract	23	'	'
Purchase Power Contract, MEAN, 10 M W [Member]	'	'	'
Sales Capacity Commitments [Abstract]	'	'	'
Long-term Contract To Sell Electric Power, Date of Contract Expiration	31-May-23	'	'
Purchase Power Contract, MEAN, 10 M W [Member] | Wygen I I I Generating Facility [Member]	'	'	'
Sales Capacity Commitments [Abstract]	'	'	'
Number of MW Sold Under Long-Term Contract	10	'	'
Purchase Power Contract, MEAN, 10 M W [Member] | Neil Simpson I I [Member]	'	'	'
Sales Capacity Commitments [Abstract]	'	'	'
Number of MW Sold Under Long-Term Contract	10	'	'
Purchase Power Contract, MEAN, 5 M W [Member]	'	'	'
Sales Capacity Commitments [Abstract]	'	'	'
Long-term Contract To Sell Electric Power, Date of Contract Expiration	1-Apr-15	'	'
Purchase Power Contract, MEAN, 5 M W [Member] | Wygen I I I Generating Facility [Member]	'	'	'
Sales Capacity Commitments [Abstract]	'	'	'
Number of MW Sold Under Long-Term Contract	5	'	'
Purchase Power Contract, MEAN, 5 M W [Member] | Neil Simpson I I [Member]	'	'	'
Sales Capacity Commitments [Abstract]	'	'	'
Number of MW Sold Under Long-Term Contract	5	'	'
Gas Transportation Purchase Contract [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	31-Oct-19	'	'
Cost of Purchased Power	633	633	633
PacifiCorp Purchase Power Agreement [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	31-Dec-23	'	'
Number of M W Capacity Purchased Under Long-term Contract	50	'	'
Cost of Purchased Power	13,026	13,224	12,515
PacifiCorp Transmission [Member]	'	'	'
Long-term Purchase Commitment [Line Items]	'	'	'
Long-term Contract for Purchase of Electric Power, Date of Contract Expiration	31-Dec-23	'	'
Number of M W Capacity Purchased Under Long-term Contract	50	'	'
Cost of Purchased Power	$1,384	$1,215	$1,215

Commitment_and_Contingencies_L

Commitment and Contingencies Legal Proceedings (Details) (Loss from Catastrophes [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Loss from Catastrophes [Member]	'
Loss Contingencies [Line Items]	'
Loss Contingency, Damages Sought, Value	$15

Quarterly_Historical_Data_Unau2

Quarterly Historical Data (Unaudited) Quarterly Financial information Data (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Revenue	$66,110	$67,268	$60,832	$59,817	$61,533	$61,134	$58,372	$62,270	$254,027	$243,309	$245,631
Operating Income (Loss)	16,844	18,704	14,293	12,503	15,619	15,361	13,859	12,742	62,344	57,581	54,720
Net income	$8,641	$9,298	$6,652	$5,582	$6,159	$8,147	$6,727	$6,053	$30,173	$27,086	$27,097

Schedule_II_Schedule_of_Valuat1

Schedule II - Schedule of Valuation and Qualifying Accounts Schedule II Consolidated Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Movement in Valuation Allowances and Reserves [Roll Forward]	'	'	'
Allowance for doubtful accounts, balance at beginning of year	$102	$143	$230
Valuation Allowances and Reserves, Additions Charged to Cost and Expense	754	503	551
Valuation Allowances and Reserves, Deductions	-636	-544	-638
Allowance for doubtful accounts, balance at end of year	$220	$102	$143