Oglethorpe Power 10-Q 7 Nov 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014
Document and Entity Information	'
Entity Registrant Name	'OGLETHORPE POWER CORP
Entity Central Index Key	'0000788816
Document Type	'10-Q
Document Period End Date	30-Sep-14
Amendment Flag	'false
Current Fiscal Year End Date	'--12-31
Entity Current Reporting Status	'Yes
Entity Filer Category	'Non-accelerated Filer
Entity Common Stock, Shares Outstanding	0
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'Q3

Condensed_Balance_Sheets

Condensed Balance Sheets (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Electric plant:	'	'
In service	$8,307,346	$8,050,103
Less: Accumulated provision for depreciation	-3,729,922	-3,615,375
Total in service	4,577,424	4,434,728
Nuclear fuel, at amortized cost	339,697	341,012
Construction work in progress	2,277,147	2,212,224
Total electric plant	7,194,268	6,987,964
Investments and funds:	'	'
Nuclear decommissioning trust fund	355,832	343,698
Investment in associated companies	65,496	66,437
Long-term investments	83,689	81,720
Restricted cash and investments	96,432	34,975
Other	16,884	16,098
Total investments and funds	618,333	542,928
Current assets:	'	'
Cash and cash equivalents	312,206	408,193
Restricted cash and short-term investments	247,699	272,686
Receivables	134,573	128,992
Inventories, at average cost	263,795	286,168
Prepayments and other current assets	31,439	16,894
Total current assets	989,712	1,112,933
Deferred charges:	'	'
Deferred debt expense, being amortized	98,695	57,175
Regulatory assets	412,456	331,108
Other	51,786	63,104
Total deferred charges	562,937	451,387
Total assets	9,365,250	9,095,212
Capitalization:	'	'
Patronage capital and membership fees	765,361	714,489
Accumulated other comprehensive margin (deficit)	160	-549
Total patronage capital and membership fees and accumulated other comprehensive margin	765,521	713,940
Long-term debt	6,881,522	6,817,518
Obligation under capital leases	102,280	121,731
Other	16,166	15,379
Total capitalization	7,765,489	7,668,568
Current liabilities:	'	'
Long-term debt and capital leases due within one year	299,960	152,153
Short-term borrowings	264,624	279,407
Accounts payable	67,809	101,529
Accrued interest	52,837	58,193
Member power bill prepayments, current	100,430	82,405
Other current liabilities	45,354	42,253
Total current liabilities	831,014	715,940
Deferred credits and other liabilities:	'	'
Gain on sale of plant, being amortized	21,047	22,157
Asset retirement obligations	426,212	408,050
Member power bill prepayments, non-current	71,819	32,313
Power sale agreement, being amortized	16,028	26,107
Regulatory liabilities	167,250	158,789
Other	66,391	63,288
Total deferred credits and other liabilities	768,747	710,704
Total equity and liabilities	$9,365,250	$9,095,212

Condensed_Statements_of_Revenu

Condensed Statements of Revenues and Expenses (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Operating revenues:	'	'	'	'
Sales to Members	$338,740	$315,646	$1,011,615	$908,490
Sales to non-Members	30,665	34,079	81,073	71,498
Total operating revenues	369,405	349,725	1,092,688	979,988
Operating expenses:	'	'	'	'
Fuel	147,314	138,252	413,566	351,467
Production	95,570	88,689	302,658	272,703
Depreciation and amortization	41,784	40,779	123,902	116,440
Purchased power	15,603	12,989	51,981	40,373
Accretion	6,198	5,755	18,324	17,062
Deferral of Hawk Road and Smith Energy Facilities effect on net margin	-7,749	-7,005	-27,885	-25,672
Total operating expenses	298,720	279,459	882,546	772,373
Operating margin	70,685	70,266	210,142	207,615
Other income:	'	'	'	'
Investment income	8,494	8,353	26,921	23,778
Other	1,956	2,317	6,565	6,834
Total other income	10,450	10,670	33,486	30,612
Interest charges:	'	'	'	'
Interest expense	88,395	80,569	256,277	232,597
Allowance for debt funds used during construction	-25,921	-23,597	-76,035	-73,013
Amortization of debt discount and expense	4,208	3,860	12,514	12,013
Net interest charges	66,682	60,832	192,756	171,597
Net margin	$14,453	$20,104	$50,872	$66,630

Condensed_Statements_of_Compre

Condensed Statements of Comprehensive Margin (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Condensed Statements of Comprehensive Margin	'	'	'	'
Net margin	$14,453	$20,104	$50,872	$66,630
Other comprehensive margin:	'	'	'	'
Unrealized gain (loss) on available-for-sale securities	-118	205	709	-1,097
Total comprehensive margin	$14,335	$20,309	$51,581	$65,533

Condensed_Statements_of_Patron

Condensed Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive Margin (Deficit) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Increase (Decrease) in Members' Capital	'	'	'	'
Balance	'	'	$713,940	$673,912
Components of comprehensive margin:	'	'	'	'
Net margin	14,453	20,104	50,872	66,630
Unrealized gain (loss) on available-for-sale securities	-118	205	709	-1,097
Balance	765,521	739,445	765,521	739,445
Patronage Capital and Membership Fees	'	'	'	'
Increase (Decrease) in Members' Capital	'	'	'	'
Balance	'	'	714,489	673,009
Components of comprehensive margin:	'	'	'	'
Net margin	'	'	50,872	66,630
Balance	765,361	739,639	765,361	739,639
Accumulated Other Comprehensive Margin (Deficit)	'	'	'	'
Increase (Decrease) in Members' Capital	'	'	'	'
Balance	'	'	-549	903
Components of comprehensive margin:	'	'	'	'
Unrealized gain (loss) on available-for-sale securities	'	'	709	-1,097
Balance	$160	($194)	$160	($194)

Condensed_Statements_of_Cash_F

Condensed Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:	'	'
Net margin	$50,872	$66,630
Adjustments to reconcile net margin to net cash provided by operating activities:	'	'
Depreciation and amortization, including nuclear fuel	233,041	218,425
Accretion cost	18,324	17,062
Amortization of deferred gains	-1,341	-1,341
Allowance for equity funds used during construction	-968	-1,938
Deferred outage costs	-41,931	-33,347
Deferral of Hawk Road and Smith Energy Facilities effect on net margin	-27,885	-25,672
Gain on sale of investments	-13,384	-21,694
Regulatory deferral of costs associated with nuclear decommissioning	2,690	10,652
Other	11,967	-5,416
Change in operating assets and liabilities:	'	'
Receivables	-5,300	-2,995
Inventories	22,373	-13,684
Prepayments and other current assets	-15,299	-234
Accounts payable	4,493	-76,892
Accrued interest	-5,356	-9,292
Accrued taxes	4,628	19,601
Other current liabilities	-4,109	-4,264
Member power bill prepayments	57,531	2,091
Total adjustments	239,474	71,062
Net cash provided by operating activities	290,346	137,692
Cash flows from investing activities:	'	'
Property additions	-428,585	-414,493
Activity in decommissioning trust fund - Purchases	-101,090	-479,622
Activity in decommissioning trust fund - Proceeds	97,475	475,446
Decrease (increase) in restricted cash and investments	-61,457	-22,111
Decrease (increase) in restricted cash and short-term investments	24,987	-190,184
Activity in other long-term investments - Purchases	-17,006	-34,510
Activity in other long-term investments - Proceeds	17,394	36,753
Activity on interest rate options - Collateral returned	-81,070	-146,730
Activity on interest rate options - Collateral received	46,100	168,840
Other	-3,053	11,563
Net cash used in investing activities	-506,305	-595,048
Cash flows from financing activities:	'	'
Long-term debt proceeds	1,009,320	875,640
Long-term debt payments	-369,253	-313,983
(Decrease) increase in short-term borrowings, net	-479,783	34,332
Other	-40,312	-559
Net cash provided by financing activities	119,972	595,430
Net decrease in cash and cash equivalents	-95,987	138,074
Cash and cash equivalents at beginning of period	408,193	298,565
Cash and cash equivalents at end of period	312,206	436,639
Cash paid for -	'	'
Interest (net of amounts capitalized)	182,059	165,388
Supplemental disclosure of non-cash investing and financing activities:	'	'
Change in plant expenditures included in accounts payable	($33,157)	$19,488

General

General	9 Months Ended
	Sep. 30, 2014
General	'
General	'
	(A)General.    The condensed financial statements included in this report have been prepared by us pursuant to the rules and regulations of the Securities and Exchange Commission. In the opinion of management, the information furnished in this report reflects all adjustments (which include only normal recurring adjustments) and estimates necessary to fairly state, in all material respects, the results for the three- and nine- month periods ended September 30, 2014 and 2013. Certain information and footnote disclosures normally included in financial statements prepared in accordance with generally accepted accounting principles have been condensed or omitted pursuant to SEC rules and regulations, although we believe that the disclosures are adequate to make the information presented not misleading. Certain prior year amounts have been reclassified to conform with the current year presentation. These condensed financial statements should be read in conjunction with the financial statements and the notes thereto included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2013, as filed with the SEC. The results of operations for the three- and nine- month periods ended September 30, 2014 are not necessarily indicative of results to be expected for the full year. As noted in our 2013 Form 10-K, our revenues consist primarily of sales to our 38 electric distribution cooperative members and, thus, the receivables on the condensed balance sheets are principally from our members. (See "Notes to Financial Statements" in our 2013 Form 10-K.)

Fair_Value

Fair Value	9 Months Ended
	Sep. 30, 2014
Fair Value	'
Fair Value	'
	(B)Fair Value.    Authoritative guidance regarding fair value measurements for financial and non-financial assets and liabilities defines fair value, establishes a framework for measuring fair value in accordance with generally accepted accounting principles, and expands disclosures about fair value measurements.
	The guidance establishes a three-tier fair value hierarchy which prioritizes the inputs used in measuring fair value as follows:
	•Level 1.  Quoted prices from active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Quoted prices in active markets provide the most reliable evidence of fair value and are used to measure fair value whenever available. Level 1 primarily consists of financial instruments that are exchange-traded.
	•Level 2.  Pricing inputs other than quoted prices in active markets included in Level 1, which are either directly or indirectly observable as of the reporting date. Level 2 includes financial instruments that are valued using models or other valuation methodologies. These models are primarily industry-standard models that consider various assumptions, including quoted forward prices for commodities, time value, volatility factors, and current market and contractual prices for the underlying instruments, as well as other relevant economic measures. Level 2 primarily consists of financial instruments that are non-exchange-traded but have significant observable inputs.
	•Level 3.  Pricing inputs that include significant inputs which are generally less observable from objective sources. These inputs may include internally developed methodologies that result in management's best estimate of fair value. Level 3 financial instruments are those whose fair value is based on significant unobservable inputs.
	As required by the guidance, assets and liabilities measured at fair value are based on one or more of the following three valuation techniques:
	1.    Market approach.    The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities (including a business) and deriving fair value based on these inputs.
	2.    Income approach.    The income approach uses valuation techniques to convert future amounts (for example, cash flows or earnings) to a single present amount (discounted). The measurement is based on the value indicated by current market expectations about those future amounts.
	3.    Cost approach.    The cost approach is based on the amount that currently would be required to replace the service capacity of an asset (often referred to as current replacement cost). This approach assumes that the fair value would not exceed what it would cost a market participant to acquire or construct a substitute asset or comparable utility, adjusted for obsolescence.
	The tables below detail assets and liabilities measured at fair value on a recurring basis at September 30, 2014 and December 31, 2013.
		Fair Value Measurements at Reporting Date Using
			September 30,			Quoted Prices in		Significant Other			Significant
			2014			Active Markets for		Observable			Unobservable
						Identical Assets		Inputs			Inputs
						(Level 1)		(Level 2)			(Level 3)
			(dollars in thousands)
	Nuclear decommissioning trust funds:
	Domestic equity	$	151,485		$	151,485	$	—		$	—
	International equity trust		72,518			—		72,518			—
	Corporate bonds		39,713			—		39,713			—
	US Treasury and government agency securities		62,440			62,440		—			—
	Agency mortgage and asset backed securities		16,736			—		16,736			—
	Other		12,940			12,940		—			—
	Long-term investments:
	International equity trust		11,166			—		11,166			—
	Corporate bonds		6,558			—		6,558			—
	US Treasury and government agency securities		13,933			13,933		—			—
	Agency mortgage and asset backed securities		570			—		570			—
	Mutual funds		51,045			51,045		—			—
	Other		417			417		—			—
	Interest rate options		13,110			—		—			13,110	-1
	Natural gas swaps		(1,764	)		—		(1,764	)		—
		Fair Value Measurements at Reporting Date Using
			December 31,			Quoted Prices in		Significant Other			Significant
			2013			Active Markets for		Observable			Unobservable
						Identical Assets		Inputs			Inputs
						(Level 1)		(Level 2)			(Level 3)
			(dollars in thousands)
	Nuclear decommissioning trust funds:
	Domestic equity	$	143,929		$	143,929	$	—		$	—
	International equity trust		72,466			—		72,466			—
	Corporate bonds		39,863			—		39,863			—
	US Treasury and government agency securities		44,846			44,846		—			—
	Agency mortgage and asset backed securities		30,133			—		30,133			—
	Municipal Bonds		641			—		641			—
	Other		11,820			11,820		—			—
	Long-term investments:
	Corporate bonds		6,487			—		6,487			—
	US Treasury and government agency securities		8,563			8,563		—			—
	Agency mortgage and asset backed securities		3,679			—		3,679			—
	International equity trust		11,148			—		11,148			—
	Mutual funds		51,559			51,559		—			—
	Other		284			284		—			—
	Interest rate options		63,471			—		—			63,471	-1
	Natural gas swaps		1,011			—		1,011			—
	(1)Interest rate options as reflected on the unaudited condensed Balance Sheet include the fair value of the interest rate options offset by $0 and $34,970,000 of collateral received from the counterparties at September 30, 2014 and December 31, 2013, respectively.
	The Level 2 investments above in corporate bonds and agency mortgage and asset backed securities may not be exchange traded. The fair value measurements for these investments are based on a market approach, including the use of observable inputs. Common inputs include reported trades and broker/dealer bid/ask prices. The fair value of the Level 2 investments above in international equity trust are calculated based on the net asset value per share of the fund. There are no unfunded commitments for the international equity trust and redemption may occur daily with a 3-day redemption notice period.
	The following tables present the changes in Level 3 assets measured at fair value on a recurring basis during the three and nine months ended September 30, 2014 and 2013.
	Three Months Ended
	September 30, 2014
			Interest rate options
			(dollars in thousands)
	Assets (Liabilities):
Balance at June 30, 2014	$	18,535
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(5,425	)
Balance at September 30, 2014	$	13,110
Three Months Ended
September 30, 2013
		Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at June 30, 2013	$	43,680
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(149	)
Balance at September 30, 2013	$	43,531
Nine Months Ended
September 30, 2014
		Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at December 31, 2013	$	63,471
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		(50,361	)
Balance at September 30, 2014	$	13,110
Nine Months Ended
September 30, 2013
		Interest rate options
		(dollars in thousands)
Assets (Liabilities):
Balance at December 31, 2012	$	25,783
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)		17,748
Balance at September 30, 2013	$	43,531
We estimate the value of the interest rate options as the sum of time value and any intrinsic value minus a counterparty credit adjustment. Intrinsic value is the value of the underlying swap, which we are able to calculate based on the forward LIBOR swap rates, the fixed rate on the underlying swap, the time to expiration, the term of the underlying swap and discount rates, all of which we are able to effectively observe. Time value is the additional value of the swaption due to the fact that it is an option. We estimate the time value using an option pricing model which, in addition to the factors used to calculate intrinsic value, also takes into account option volatility, which we estimate based on option valuations we obtain from various sources. We estimate the counterparty credit adjustment by observing credit attributes, including the credit default swap spread of entities similar to the counterparty and the amount of credit support that is available for each swaption. Since the primary component of the LIBOR swaptions' value is time value, which is based on estimated option volatility derived from valuations of comparable instruments that are generally not publicly available, we have categorized these LIBOR swaptions as Level 3. We believe the estimated fair values for the LIBOR swaptions we hold are based on the most accurate information available for these types of derivative contracts. For additional information regarding our interest rate options, see Note C.
The estimated fair values of our long-term debt, including current maturities at September 30, 2014 and December 31, 2013 were as follows (in thousands):
2014				2013
		Carrying			Fair		Carrying			Fair
		Value			Value		Value			Value
Long-term debt	$	7,157,870		$	7,983,009	$	6,954,293		$	7,317,476
The estimated fair value of long-term debt is classified as Level 2 and is estimated based on observed or quoted market prices for the same or similar issues or on current rates offered to us for debt of similar maturities. The primary sources of our long-term debt consist of first mortgage bonds, pollution control revenue bonds and long-term debt issued by the Federal Financing Bank that is guaranteed by the Rural Utilities Service or the U.S. Department of Energy. We also have small amounts of long-term debt provided by National Rural Utilities Cooperative Finance Corporation (CFC) and by CoBank, ACB. The valuations for the first mortgage bonds and the pollution control revenue bonds were obtained from third party investment banking firms and a third party subscription service, and are based on secondary market trading of our debt. Valuations for debt issued by the Federal Financing Bank are based on U.S. Treasury rates as of September 30, 2014 plus an applicable spread, which reflects our borrowing rate for new loans of this type from the Federal Financing Bank. We use an interest rate quote sheet provided by CoBank for valuation of the CoBank debt, which reflects current rates for a similar loan. The rates on the CFC debt are fixed and the valuation is based on rate quotes provided by CFC.
For cash and cash equivalents, restricted cash and receivables, the carrying amount approximates fair value because of the short-term maturity of those instruments.

Derivative_Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2014
Derivative Instruments	'
Derivative Instruments	'
	(C)Derivative Instruments.    Our risk management and compliance committee provides general oversight over all risk management and compliance activities, including but not limited to, commodity trading, investment portfolio management and interest rate risk management. We use commodity trading derivatives to manage our exposure to fluctuations in the market price of natural gas. To hedge the risk of rising interest rates on long-term debt in connection with capital expenditures, we have entered into interest rate options. We do not apply hedge accounting for any of these derivatives, but apply regulatory accounting. Consistent with our rate-making, unrealized gains or losses on our natural gas swaps and interest rate options are reflected as regulatory assets or liabilities, as appropriate.
	We are exposed to credit risk as a result of entering into these hedging arrangements. Credit risk is the potential loss resulting from a counterparty's nonperformance under an agreement. We have established policies and procedures to manage credit risk through counterparty analysis, exposure calculation and monitoring, exposure limits, collateralization and certain other contractual provisions.
	It is possible that volatility in commodity prices and/or interest rates could cause us to have credit risk exposures with one or more counterparties. We currently have credit risk exposure to our interest rate options counterparties. If such counterparties fail to perform their obligations, we could suffer a financial loss. However, as of September 30, 2014, all of the counterparties with transaction amounts outstanding under our hedging programs are rated investment grade by the major rating agencies or have provided a guaranty from one of their affiliates that is rated investment grade.
	We have entered into International Swaps and Derivatives Association agreements with our natural gas hedge and interest rate option counterparties that mitigate credit exposure by creating contractual rights relating to creditworthiness, collateral, termination and netting (which, in certain cases, allows us to use the net value of affected transactions with the same counterparty in the event of default by the counterparty or early termination of the agreement).
	Additionally, we have implemented procedures to monitor the creditworthiness of our counterparties and to evaluate nonperformance in valuing counterparty positions. We have contracted with a third party to assist in monitoring certain of our counterparties' credit standing and condition. Net liability positions are generally not adjusted as we use derivative transactions as hedges and have the ability and intent to perform under each of our contracts. In the instance of net asset positions, we consider general market conditions and the observable financial health and outlook of specific counterparties, forward looking data such as credit default swaps, when available, and historical default probabilities from credit rating agencies in evaluating the potential impact of nonperformance risk to derivative positions.
	The contractual agreements contain provisions that could require us or the counterparty to post collateral or credit support. The amount of collateral or credit support that could be required is calculated as the difference between the aggregate fair value of the hedges and pre-established credit thresholds. The credit thresholds are contingent upon each party's credit ratings from the major credit rating agencies. The collateral and credit support requirements vary by contract and by counterparty.
	Gas hedges.    Under our natural gas swap arrangements, we pay the counterparty a fixed price for specified natural gas quantities and receive a payment for such quantities based on a market price index. These payment obligations are netted, such that if the market price index is lower than the fixed price, we will make a net payment, and if the market price index is higher than the fixed price, we will receive a net payment.
	At September 30, 2014 and December 31, 2013, the fair value of our natural gas contracts were a net liability of approximately $1,764,000 and $1,011,000, respectively.
	As of September 30, 2014 and December 31, 2013, neither we nor any counterparties were required to post credit support or collateral under these natural gas swap agreements. If the credit-risk-related contingent features underlying these agreements had been triggered on September 30, 2014 due to our credit rating being downgraded below investment grade, we would have been required to post letters of credit in the amount of $2,022,000 with our counterparties.
	The following table reflects the volume activity of our natural gas derivatives as of September 30, 2014 that is expected to settle or mature each year:
	Year		Natural Gas Swaps
			(MMBTUs)
			(in millions)
	2014		0.4
	2015		7.9
	2016		5.4
	Total		14.3
	Interest rate options.     We are exposed to the risk of rising interest rates when we incur long-term debt in connection with capital expenditures, particularly the construction of Vogtle Units No. 3 and No. 4. In the fourth quarter of 2011, we purchased LIBOR swaptions at a cost of $100,000,000 with a total notional amount of approximately $2,200,000,000 to hedge the interest rates on a portion of the debt that we are incurring to finance two additional nuclear units at Plant Vogtle. Since 2013, swaptions having a notional amount of approximately $1,174,248,000 have expired and as of September 30, 2014, the remaining notional amount of our outstanding swaptions was approximately $1,004,955,000.
	The LIBOR swaptions are each designed to cap our effective interest rate at a specified fixed interest rate on a specified option expiration date. This is accomplished by means of a payment of the cash settlement value our counterparties are obligated to make to us if prevailing fixed LIBOR swap rates exceed the specified fixed rate on the option expiration date. This payment would partially offset our interest costs, thereby reducing our effective interest rate. The cash settlement value would be zero if swap rates are at or below the specified fixed rate on the expiration date. The cash settlement value is calculated based on the value of an underlying swap which we have the right, but not the obligation, to enter into, which would begin on the option expiration date and extend until 2042 and under which we would pay the specified fixed rate and receive a floating LIBOR rate. The fixed rates on the unexpired swaptions we hold average 107 basis points above the corresponding LIBOR swap rates that were in effect as of September 30, 2014 and the weighted average fixed rate is 4.08%. Swaptions having notional amounts totaling $419,796,000 expired without value during the nine months ended September 30, 2014. The remaining swaptions expire quarterly through 2017.
	We paid all the premiums to purchase these LIBOR swaptions at the time we entered into these transactions and have no additional payment obligations. These derivatives are recorded at fair value. At September 30, 2014 and December 31, 2013, the fair value of these swaptions was approximately $13,110,000 and $63,471,000, respectively. To manage our credit exposure to our counterparties, we negotiated credit support provisions that require each counterparty to provide us collateral in the form of cash or securities to the extent that the value of the swaptions outstanding for that counterparty exceeds a certain threshold. The collateral thresholds can range from $0 to $10,000,000 depending on each counterparty's credit rating. As of September 30, 2014, and December 31, 2013, we held $0 and $34,970,000 of funds posted as collateral by the counterparties, respectively. The collateral received is recorded as restricted cash on our balance sheet. The liability associated with the collateral is recorded as an offset to the fair values of the swaptions, which are recorded within other deferred charges on the balance sheet, resulting in a net carrying amount of the interest rate options of $13,110,000 and $28,501,000 at September 30, 2014 and December 31, 2013, respectively.
	We are deferring unrealized gains or losses from the change in fair value of each LIBOR swaption and related carrying and other incidental costs in accordance with our rate-making treatment. The realized deferred costs and deferred gains, if any, from the settlement of the interest rate options will be amortized and collected in rates over the life of the $2.2 billion of debt that we hedged with the swaptions.
	The following table reflects the remaining notional amount of forecasted debt issuances we have hedged in each year with LIBOR swaptions as of September 30, 2014.
	Year		LIBOR Swaption
			Notional Dollar
			Amount
			(in thousands)
	2014	$	143,629
	2015		470,624
	2016		310,533
	2017		80,169
	Total	$	1,004,955
	The table below reflects the fair value of derivative instruments and their effect on our condensed balance sheets at September 30, 2014 and December 31, 2013.
		Balance Sheet			Fair Value
		Location
					2014			2013
					(dollars in thousands)
	Not designated as hedges:
	Assets:
	Interest rate options(1)	Other deferred charges		$	13,110		$	63,471
	Natural gas swaps	Other current assets		$	258		$	1,011
	Liabilities:
	Natural gas swaps	Other current liabilities		$	2,022		$	—
	(1)Excludes liability associated with cash collateral of $0 and $34,970,000 as of September 30, 2014 and December 31, 2013, respectively, which is recorded as an offset to the fair value of the swaptions on the unaudited condensed balance sheets.
	The following table presents the gross realized gains and (losses) on derivative instruments recognized in margin for the three and nine months ended September 30, 2014 and 2013.
		Statement of			Three months ended						Nine months ended
		Revenues and			September 30,						September 30,
		Expenses
		Location			2014			2013			2014			2013
					(dollars in thousands)
	Not Designated as hedges:
	Natural Gas Swaps	Fuel			638			122			1,874			688
				$			$			$			$
	Natural Gas Swaps	Fuel			(889	)		(3,089	)		(890	)		(4,002	)
				$	(251	)	$	(2,967	)	$	984		$	(3,314	)
	The following table presents the unrealized gains and (losses) on derivative instruments deferred on the balance sheet at September 30, 2014 and December 31, 2013.
		Balance Sheet			2014			2013
		Location
					(dollars in thousands)
	Not designated as hedges:
	Natural gas swaps	Regulatory liability						1,011
				$	—		$
	Natural gas swaps	Regulatory asset		$	(1,764	)	$	—
	Interest rate options	Regulatory asset			(47,598	)		(15,003	)
			$	(49,362	)	$	(13,992	)
The following table presents the gross amounts of derivatives and their related offset amounts as permitted by their respective master netting agreements and obligations to return cash collateral.
Gross Amounts	Gross	Cash	Net Amounts of
of Recognized	Amounts	Collateral	Assets Presented on
Assets	offset on the		the Balance Sheet
(Liabilities)	Balance Sheet
		(dollars in thousands)
September 30, 2014
Assets:
Natural gas swaps	$	261		$	(2,025	)	$	—		$	(1,764	)
Interest rate options	$	13,110		$	—		$	—		$	13,110
December 31, 2013
Assets:
Natural gas swaps	$	1,069		$	(58	)	$	—		$	1,011
Interest rate options	$	63,471		$	—		$	(34,970	)	$	28,501

Investments_in_Debt_and_Equity

Investments in Debt and Equity Securities	9 Months Ended
	Sep. 30, 2014
Investments in Debt and Equity Securities	'
Investments in Debt and Equity Securities	'
	(D)Investments in Debt and Equity Securities.    Investment securities we hold are classified as available-for-sale. Available-for-sale securities are carried at market value with unrealized gains and losses, net of any tax effect, added to or deducted from other comprehensive margin, except that, in accordance with our rate-making treatment, unrealized gains and losses from investment securities held in the nuclear decommissioning funds are directly added to or deducted from the regulatory asset for asset retirement obligations. Realized gains and losses on the nuclear decommissioning funds are also recorded to the regulatory asset. All realized and unrealized gains and losses are determined using the specific identification method. As of September 30, 2014, approximately 79% of these gross unrealized losses were in effect for less than one year.
	The following tables summarize the activities for available-for-sale securities as of September 30, 2014 and December 31, 2013.
	Gross Unrealized
			(dollars in thousands)
	September 30, 2014		Cost		Gains		Losses			Fair
										Value
	Equity	$	196,523	$	64,560	$	(2,185	)	$	258,898
	Debt		166,710		9,159		(8,417	)		167,452
	Other		13,173		—		(2	)		13,171
	Total	$	376,406	$	73,719	$	(10,604	)	$	439,521
	Gross Unrealized
			(dollars in thousands)
	December 31, 2013		Cost		Gains		Losses			Fair
										Value
	Equity	$	182,755	$	68,424	$	(1,053	)	$	250,126
	Debt		164,941		7,319		(9,070	)		163,190
	Other		12,101		2		—			12,103
	Total	$	359,797	$	75,745	$	(10,123	)	$	425,419

Recently_Issued_or_Adopted_Acc

Recently Issued or Adopted Accounting Pronouncements	9 Months Ended
	Sep. 30, 2014
Recently Issued or Adopted Accounting Pronouncements	'
Recently Issued or Adopted Accounting Pronouncements	'
	(E)Recently Issued or Adopted Accounting Pronouncements.    In May 2014, the Financial Accounting Standards Board issued "Revenue from Contracts with Customers" (Topic 606). The new revenue standard requires that an entity recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods and services. The standard is effective for the annual reporting period beginning after December 15, 2016 and early adoption is not permitted. We are currently evaluating the future impact of this standard to our consolidated financial position or results of operations.

Accumulated_Comprehensive_Marg

Accumulated Comprehensive Margin (Deficit)	9 Months Ended
	Sep. 30, 2014
Accumulated Comprehensive Margin (Deficit)	'
Accumulated Comprehensive Margin (Deficit)	'
	(F)Accumulated Comprehensive Margin (Deficit).    The table below provides detail of the beginning and ending balance for each classification of other comprehensive margin (deficit) along with the amount of any reclassification adjustments included in margin for each of the periods presented in the unaudited Condensed Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive Margin (Deficit). There were no material changes in the nature, timing or amounts of expected (gain) loss reclassified to net margin from the amounts disclosed in our 2013 Form 10-K. Amounts reclassified to net margin in the table below are reflected in "Other income" on our unaudited Condensed Statement of Revenues and Expenses.
	Our effective tax rate is zero; therefore, all amounts below are presented net of tax.
		Accumulated Other
		Comprehensive Margin
		(Deficit)
		Three Months Ended
			(dollars in thousands)
			Available-for-sale Securities
	Balance at June 30, 2013	$	(399	)
	Unrealized gain		181
	Loss reclassified to net margin		24
	Balance at September 30, 2013	$	(194	)
	Balance at June 30, 2014		278
		$
	Unrealized (loss)		(100
				)
	(Gain) reclassified to net margin		(18
				)
	Balance at September 30, 2014	$	160
		Nine Months Ended
			(dollars in thousands)
			Available-for-sale
			Securities
	Balance at December 31, 2012	$	903
	Unrealized (loss)		(1,041
				)
	(Gain) reclassified to net margin		(56
				)
	Balance at September 30, 2013	$	(194	)
	Balance at December 31, 2013		(549
		$		)
	Unrealized gain		782
	(Gain) reclassified to net margin		(73
				)
	Balance at September 30, 2014	$	160

Contingencies_and_Regulatory_M

Contingencies and Regulatory Matters	9 Months Ended
	Sep. 30, 2014
Contingencies and Regulatory Matters	'
Contingencies and Regulatory Matters	'
	(G)Contingencies and Regulatory Matters.
	We do not anticipate that the liabilities, if any, for any current proceedings against us will have a material effect on our financial condition or results of operations. However, at this time, the ultimate outcome of any pending or potential litigation cannot be determined.
	a.    Nuclear Construction
	In April 2008, Georgia Power Company, acting for itself and as agent for us, the Municipal Electric Authority of Georgia, and the City of Dalton, Georgia (collectively, the Co-owners), and Westinghouse Electric Company LLC and Stone & Webster, Inc. (collectively, the Contractor) entered into an engineering, procurement, and construction agreement to design, engineer, procure, and construct two AP1000 nuclear units with electric generating capacity of approximately 1,100 megawatts each and related facilities, structures, and improvements at Plant Vogtle (Vogtle Units No. 3 and No. 4).
	Under the agreement, the Co-Owners and the Contractor have established both informal and formal dispute resolution procedures in order to resolve issues arising during the course of constructing a project of this magnitude. Georgia Power, on behalf of the Co-owners, has successfully initiated both formal and informal claims through these procedures, including ongoing claims. When matters are not resolved through these procedures, the parties may proceed to litigation. The Contractor and the Co-owners are involved in litigation with respect to certain claims that have not been resolved through the formal dispute resolution process.
	Current litigation relates to costs associated with design changes to the Westinghouse AP1000 Design Control Document (DCD) and costs associated with delays in the project schedule related to the timing of approval of the DCD and issuance of the combined construction permits and operating licenses by the Nuclear Regulatory Commission. In July 2012, the Co-owners and Contractor began negotiations regarding these costs, including the assertion by the Contractor that the Co-owners are responsible for these costs under the terms of the agreement. On November 1, 2012, the Co-owners filed suit against the Contractor in the U.S. District Court for the Southern District of Georgia, seeking a declaratory judgment that the Co-owners are not responsible for these costs. Also on November 1, 2012, the Contractor filed suit against the Co-owners in the U.S. District Court for the District of Columbia alleging the Co-owners are responsible for these costs. In August 2013, the U.S. District Court for the District of Columbia dismissed the Contractor's suit, ruling that proper venue is the U.S. District Court for the Southern District of Georgia. In September 2013, the Contractor appealed the decision to the U.S. Court of Appeals for the District of Columbia.
	The portion of the additional costs claimed by the Contractor in its initial complaint that would be attributable to us, based on our ownership interest, was approximately $280 million in 2008 dollars with respect to these issues. The Contractor has also asserted that it is entitled to further schedule extensions. On May 22, 2014, the Contractor filed an amended counterclaim to the lawsuit pending in the Southern District of Georgia alleging that (i) the design changes to the DCD imposed by the Nuclear Regulatory Commission have delayed module production and the impacts to the Contractor are recoverable by the Contractor under the agreement and (ii) the changes to the basemat rebar design required by the Nuclear Regulatory Commission caused additional costs and delays recoverable by the Contractor under the agreement. The Contractor did not specify in its amended counterclaim the amounts relating to these new allegations, but the Contractor subsequently asserted and may from time to time continue to assert that it is entitled to additional payments with respect to these new allegations, any of which could be substantial. Georgia Power, on behalf of the Co-owners, has not agreed with either the proposed cost or schedule adjustments or that the Co-owners have any responsibility for costs related to these issues.
	While litigation is ongoing and Georgia Power and the Co-owners intend to vigorously defend their positions, Georgia Power and the Co-owners also expect negotiations with the Contractor to continue with respect to cost and schedule during which time the parties will attempt to reach a mutually acceptable compromise of their positions.
	If any or all of these costs are ultimately imposed on the Co-owners, we will capitalize the costs attributable to us. As of September 30, 2014, no material amounts have been recorded related to this claim. Additional claims by the Contractor or Georgia Power, on behalf of the Co-owners, are also likely to arise throughout construction.
	b.    Patronage Capital Litigation
	On March 13, 2014, a lawsuit was filed in the Superior Court of DeKalb County, Georgia, against us, Georgia Transmission and three of our member distribution cooperatives. Plaintiffs filed an amended complaint on July 28, 2014. The amended complaint challenges the patronage capital distribution practices of Georgia's electric cooperatives and seeks to certify a defendant class of all but one of our 38 members. It was filed by four former consumer-members of four of our members on behalf of themselves and a proposed class of all former consumer-members of our members. Plaintiffs claim that approximately 30% of all the defendants' total allocated patronage capital belongs to former consumer-members. Plaintiffs also allege that patronage capital owed to former consumer-members includes patronage capital allocated by us to our members but not yet distributed to our members. Plaintiffs claim that the patronage capital of former consumer-members held by defendants and the proposed defendant class should be retired immediately when the consumer-members end their membership by terminating service, or alternatively, according to a revolving schedule of no longer than 13 years from the date of its allocation and seek relief to effect such retirements. Plaintiffs further seek to require the defendants to adjust rates in order to establish and maintain reasonable reserves to fund patronage capital retirements on this basis. Plaintiffs also claim that defendants and the proposed defendant class should be required to adopt policies to periodically retire the patronage capital of all consumer-members on a revolving schedule of no longer than 13 years from the date of its allocation. Our first mortgage indenture restricts our ability to distribute patronage capital. See "Item 1—BUSINESS—OGLETHORPE POWER CORPORATION—First Mortgage Indenture" in our 2013 Form 10-K. Although not expected, if we were ordered by the Court to make distributions of our patronage capital, our first mortgage indenture would require us to raise our rates to a level sufficient so that we could comply with the current patronage capital distribution restrictions, and the rate increases required to meet the Plaintiffs' demands would be significant for a period of years.
	On August 20, 2014, a second patronage capital lawsuit was filed in the Superior Court of DeKalb County against us, Georgia Transmission, and two of our member distribution cooperatives. The case was filed by two alleged current consumer-members of the two member distribution cooperatives named in the lawsuit. Similar to the above described litigation, this complaint challenges the patronage capital distribution practices of Georgia's electric cooperatives; however, one notable difference is that the first case, described above, seeks to bring claims on behalf of former members while this second case seeks to bring claims on behalf of current members. The plaintiffs allege that the defendants have (i) retained patronage capital for an unreasonably long period of time; (ii) conspired with each other to deprive consumer-members of their patronage capital; and (iii) breached bylaw provisions allegedly requiring that patronage capital be retired when the financial condition of the cooperative will not be impaired. The plaintiffs seek unspecified damages and equitable relief, including an order declaring that the defendants be required to retire patronage capital "according to a regular, reasonable revolving plan." Similarly to the litigation described above, although not expected, if we were ordered by the Court to make distributions of our patronage capital, our first mortgage indenture would require us to raise our rates to a level where we could comply with current patronage capital distribution restrictions and the rate increases required to meet the Plaintiff's demands could be significant for a period of years. The plaintiffs seek to certify three plaintiffs' classes but do not seek to certify a defendants' class.
	We intend to defend vigorously against all claims in the above-described litigation.
	c.    Environmental Matters
	As is typical for electric utilities, we are subject to various federal, state and local environmental laws which represent significant future risks and uncertainties. Air emissions, water discharges and water usage are extensively controlled, closely monitored and periodically reported. Handling and disposal requirements govern the manner of transportation, storage and disposal of various types of waste. We are also subject to climate change regulations that impose restrictions on emissions of greenhouse gases, including carbon dioxide, for certain new and modified facilities.
	In general, these and other types of environmental requirements are becoming increasingly stringent. Such requirements may substantially increase the cost of electric service, by requiring modifications in the design or operation of existing facilities or the purchase of emission allowances. Failure to comply with these requirements could result in civil and criminal penalties and could include the complete shutdown of individual generating units not in compliance. Certain of our debt instruments require us to comply in all material respects with laws, rules, regulations and orders imposed by applicable governmental authorities, which include current and future environmental laws or regulations. Should we fail to be in compliance with these requirements, it would constitute a default under those debt instruments. We believe that we are in compliance with those environmental regulations currently applicable to our business and operations. Although it is our intent to comply with current and future regulations, we cannot provide assurance that we will always be in compliance.
	At this time, the ultimate impact of any new and more stringent environmental regulations described above is uncertain and could have an effect on our financial condition, results of operations and cash flows as a result of future additional capital expenditures and increased operations and maintenance costs.
	Additionally, litigation over environmental issues and claims of various types, including property damage, personal injury, common law nuisance, and citizen enforcement of environmental requirements such as air quality and water standards, has increased generally throughout the United States. In particular, personal injury and other claims for damages caused by alleged exposure to hazardous materials, and common law nuisance claims for injunctive relief, personal injury and property damage allegedly caused by coal combustion residue, greenhouse gas and other emissions have become more frequent.

Restricted_cash_and_investment

Restricted cash and investments	9 Months Ended
	Sep. 30, 2014
Restricted Short-term Investments	'
Restricted cash and investments	'
	(H)Restricted Cash and Investments.    At September 30, 2014 and December 31, 2013, we had restricted cash and investments totaling $344,131,000 and $307,661,000, respectively, of which $96,432,000 and $34,975,000, respectively, was classified as long-term. Restricted cash balances consist primarily of funds posted as collateral by counterparties to our interest rate options. Restricted investments represent funds on deposit with the Rural Utilities Service in the Cushion of Credit Account. The restricted investments will be utilized for future Rural Utilities Service Federal Financing Bank debt service payments. The funds on deposit earn interest at a rate of 5% per annum.

Regulatory_Assets_and_Liabilit

Regulatory Assets and Liabilities	9 Months Ended
	Sep. 30, 2014
Regulatory Assets and Liabilities	'
Regulatory Assets and Liabilities	'
	(I)Regulatory Assets and Liabilities.    We apply the accounting guidance for regulated operations. Regulatory assets represent certain costs that are probable of recovery from our members in future revenues through rates under the wholesale power contracts with our members extending through December 31, 2050. Regulatory liabilities represent certain items of income that we are retaining and that will be applied in the future to reduce revenues required to be recovered from our members.
	The following regulatory assets and liabilities are reflected on the unaudited condensed balance sheet as of September 30, 2014 and December 31, 2013.
			2014		2013
			(dollars in thousands)
	Regulatory Assets:
	Premium and loss on reacquired debt(a)	$	74,415	$	82,499
	Amortization on capital leases(b)		11,897		16,124
	Outage costs(c)		44,911		35,155
	Interest rate swap termination fees(d)		10,343		13,336
	Depreciation expense(f)		47,294		48,362
	Deferred charges related to Vogtle Units No. 3 and No. 4 training costs(g)		31,126		27,678
	Interest rate options cost(h)		89,781		38,984
	Deferral of effects on net margin—Smith Energy Facility(i)		96,811		63,491
	Other regulatory assets(j)		5,878		5,479
	Total Regulatory Assets	$	412,456	$	331,108
	Regulatory Liabilities:
	Accumulated retirement costs for other obligations(e)	$	21,069	$	24,520
	Deferral of effects on net margin—Hawk Road Energy Facility(i)		28,605		23,379
	Major maintenance reserve(k)		26,762		28,064
	Deferred debt service adder(l)		64,375		57,223
	Asset retirement obligations(e)		21,508		19,508
	Other regulatory liabilities(j)		4,931		6,095
	Total Regulatory Liabilities	$	167,250	$	158,789
	Net Regulatory Assets		245,206		172,319
		$		$
	(a)Represents premiums paid, together with unamortized transaction costs related to reacquired debt that are being amortized over the lives of the refunding debt, which range up to 30 years.
	(b)Represents the difference between lease payments and the aggregate of the amortization on the capital lease assets and the interest on the capital lease obligations for rate-making purposes. Recovered over the remaining terms of the leases through 2031.
	(c)Consists of both coal-fired maintenance and nuclear refueling outage costs. Coal-fired outage costs are amortized on a straight-line basis to expense over an 18 to 36-month period. Nuclear refueling outage costs are amortized on a straight-line basis to expense over the 18 to 24-month operating cycles of each unit.
	(d)Represents losses on settled interest rate swap arrangements that are being amortized through 2016 and 2019.
	(e)Represents difference in timing of recognition of the costs of decommissioning for financial statement purposes and for ratemaking purposes.
	(f)Prior to Nuclear Regulatory Commission (NRC) approval of a 20-year license extension for Plant Vogtle, we deferred the difference between Plant Vogtle depreciation expense based on the then 40-year operating license and depreciation expense assuming an expected 20-year license extension. Amortization commenced upon NRC approval of the license extension in 2009 and is being amortized over the remaining life of the plant.
	(g)Deferred charges related to Vogtle Units No. 3 and No. 4 training and interest related carrying costs of such training. Amortization will commence effective with the commercial operation date of each unit and amortized to expense over the life of the units.
	(h)Deferral of net loss associated with the change in fair value of the interest rate options to hedge interest rates on certain borrowings related to Vogtle Units No. 3 and No. 4 construction. Amortization will commence in February 2020 and will be amortized through February 2044, the life of the DOE-guaranteed loan which is financing a portion of the construction project.
	(i)Effects on net margin for Smith and Hawk Road Energy Facilities are deferred until the end of 2015 and will be amortized over the remaining life of each respective plant.
	(j)The amortization period for other regulatory assets range up to 35 years and the amortization period of other regulatory liabilities range up to 18 years.
	(k)Represents collections for future major maintenance costs; revenues are recognized as major maintenance costs are incurred.
	(l)Represents collections to fund certain debt payments through the end of 2025 in excess of amounts collected through depreciation expense; the deferred credits will be amortized over the remaining useful life of the plants.

Member_Power_Bill_Prepayments

Member Power Bill Prepayments	9 Months Ended
	Sep. 30, 2014
Member Power Bill Prepayments	'
Member Power Bill Prepayments	'
	(J)Member Power Bill Prepayments.    We have a power bill prepayment program pursuant to which members can prepay their power bills from us at a discount based on our avoided cost of borrowing. The prepayments are credited against the participating members' power bills in the month(s) agreed upon in advance. The discounts are credited against the power bills and are recorded as a reduction to member revenues. The prepayments are being credited against members' power bills through January 2018, with the majority of the balance scheduled to be credited by the end of 2015.

Debt

Debt	9 Months Ended
	Sep. 30, 2014
Debt	'
Debt	'
	(K)Debt.
	a)Department of Energy Loan Guarantee:
	Pursuant to the loan guarantee program established under Title XVII of the Energy Policy Act of 2005 (the "Title XVII Loan Guarantee Program"), we and the U.S. Department of Energy, acting by and through the Secretary of Energy entered into a Loan Guarantee Agreement on February 20, 2014 (the "Loan Guarantee Agreement") pursuant to which the Department of Energy agreed to guarantee our obligations (the "Department of Energy Guarantee") under the Note Purchase Agreement dated as of February 20, 2014 (the "Note Purchase Agreement"), among us, the Federal Financing Bank and the Department of Energy and the Future Advance Promissory Note No. 1 and the Future Advance Promissory Note No. 2, each dated February 20, 2014, made by us to Federal Financing Bank (the "Federal Financing Bank Notes" and together with the Note Purchase Agreement, the "FFB Credit Facility Documents"). The FFB Credit Facility Documents provide for a multi-advance term loan facility (the "Facility"), under which we may make term loan borrowings through Federal Financing Bank.
	Proceeds of advances made under the Facility will be used to reimburse us for a portion of certain costs of construction relating to Vogtle Units No. 3 and No. 4 that are eligible for financing under the Title XVII Loan Guarantee Program ("Eligible Project Costs"). Aggregate borrowings under the Facility may not exceed the lesser of (i) 70% of Eligible Project Costs or (ii) $3,057,069,461, $335,471,604 of which is designated for capitalized interest.
	Under the Loan Guarantee Agreement, we are obligated to reimburse the Department of Energy in the event the Department of Energy is required to make any payments to the Federal Financing Bank under the Department of Energy Guarantee. Our payment obligations to the Federal Financing Bank under the Federal Financing Bank Notes and reimbursement obligations to the Department of Energy under the related reimbursement notes are secured equally and ratably with all of our other notes and obligations issued under our first mortgage indenture by a lien on substantially all of our owned tangible and certain of our intangible assets, including property we acquire in the future.
	Advances.     Advances may be requested under the Facility on a quarterly basis through December 31, 2020. On February 20, 2014, we made an initial borrowing in the principal amount of $725,000,000 at a fixed interest rate of 3.867% through February 20, 2044. In connection with the receipt of these funds, we repaid a like amount of outstanding short-term obligations, which included a $260,000,000 term loan originally due April 1, 2014 and $465,000,000 of commercial paper. These outstanding obligations were classified as long-term at December 31, 2013.
	Future advances are subject to satisfaction of customary conditions, as well as certification of compliance with the requirements of the Title XVII Loan Guarantee Program, accuracy of project-related representations and warranties, delivery of updated project-related information, certification regarding Georgia Power's compliance with certain obligations relating to the Cargo Preference Act, as amended, evidence of compliance with the prevailing wage requirements of the Davis-Bacon Act, as amended, and certification from Department of Energy's consulting engineer that proceeds of the advance are used to reimburse Eligible Project Costs.
	Maturity, Interest Rate and Amortization.     The final maturity date for each advance under the Facility is February 20, 2044. Interest is payable quarterly in arrears on February 20, May 20, August 20 and November 20 of each year. Principal and interest payments will begin on February 20, 2020. Interest accrued and payable through November 20, 2019, up to a maximum of $335,471,604, is reflected as additional borrowings under the Facility. As of September 30, 2014, $17,179,000 of interest is reflected as long-term debt on our condensed balance sheet.
	Under Future Advance Promissory Note No. 1, we may select an interest rate period applicable to each advance, with such interest rate periods ranging from three months to the final maturity date. All advances under Future Advance Promissory Note No. 2 will bear a fixed rate of interest through the final maturity date. Under both Federal Financing Bank Notes, the interest rates during the applicable interest rate periods will equal the current average yield on U.S. Treasuries of comparable maturity at the beginning of the interest rate period, plus a spread equal to 0.375%.
	In connection with our entry into the Loan Guarantee Agreement and the FFB Credit Facility Documents, we incurred issuance costs of approximately $51,000,000, which will be amortized over the life of the borrowings under the Facility. Issuance costs include fees paid to the Department of Energy, legal and consulting expenses and costs for compliance with certain federal requirements (including compliance with the Davis-Bacon Act).
	b)Rural Utilities Service Guaranteed Loans:
	For the nine month period ended September 30, 2014, we received advances on Rural Utilities Service-guaranteed Federal Financing Bank loans totaling $35,900,000 for general and environmental improvements at existing plants.
	c)Bond Issuance:
	On June 12, 2014, we issued $250,000,000 of 4.55% first mortgage bonds, Series 2014A primarily for the purpose of repaying outstanding commercial paper issued for the interim financing of general and environmental capital expenditures at our existing generation facilities and for general corporate purposes. The bonds are secured under our first mortgage indenture.

Purchase_agreements

Purchase agreements	9 Months Ended
	Sep. 30, 2014
Purchase Agreements Disclosure Abstract	'
Purchase Agreements	'
	(L)Purchase Agreements.    On April 11, 2014, we signed a precedent agreement with Transcontinental Gas Pipeline Company, LLC (Transco) for additional firm natural gas transportation to our Smith facility. The additional firm transportation is contingent upon the construction of a new natural gas pipeline by Transco. The agreement has a base term of 25 years, with a fixed charge of $37,700,000 per year for the base term. Our obligation to make payments begins when the pipeline expansion project is placed into service, which is projected to be May 1, 2017.

Fair_Value_Tables

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2014
Fair Value	'
Schedule of assets and liabilities measured at fair value on a recurring basis	'
		Fair Value Measurements at Reporting Date Using
			September 30,			Quoted Prices in		Significant Other			Significant
			2014			Active Markets for		Observable			Unobservable
						Identical Assets		Inputs			Inputs
						(Level 1)		(Level 2)			(Level 3)
			(dollars in thousands)
	Nuclear decommissioning trust funds:
	Domestic equity	$	151,485		$	151,485	$	—		$	—
	International equity trust		72,518			—		72,518			—
	Corporate bonds		39,713			—		39,713			—
	US Treasury and government agency securities		62,440			62,440		—			—
	Agency mortgage and asset backed securities		16,736			—		16,736			—
	Other		12,940			12,940		—			—
	Long-term investments:
	International equity trust		11,166			—		11,166			—
	Corporate bonds		6,558			—		6,558			—
	US Treasury and government agency securities		13,933			13,933		—			—
	Agency mortgage and asset backed securities		570			—		570			—
	Mutual funds		51,045			51,045		—			—
	Other		417			417		—			—
	Interest rate options		13,110			—		—			13,110	-1
	Natural gas swaps		(1,764	)		—		(1,764	)		—
		Fair Value Measurements at Reporting Date Using
			December 31,			Quoted Prices in		Significant Other			Significant
			2013			Active Markets for		Observable			Unobservable
						Identical Assets		Inputs			Inputs
						(Level 1)		(Level 2)			(Level 3)
			(dollars in thousands)
	Nuclear decommissioning trust funds:
	Domestic equity	$	143,929		$	143,929	$	—		$	—
	International equity trust		72,466			—		72,466			—
	Corporate bonds		39,863			—		39,863			—
	US Treasury and government agency securities		44,846			44,846		—			—
	Agency mortgage and asset backed securities		30,133			—		30,133			—
	Municipal Bonds		641			—		641			—
	Other		11,820			11,820		—			—
	Long-term investments:
	Corporate bonds		6,487			—		6,487			—
	US Treasury and government agency securities		8,563			8,563		—			—
	Agency mortgage and asset backed securities		3,679			—		3,679			—
	International equity trust		11,148			—		11,148			—
	Mutual funds		51,559			51,559		—			—
	Other		284			284		—			—
	Interest rate options		63,471			—		—			63,471	-1
	Natural gas swaps		1,011			—		1,011			—
	(1)Interest rate options as reflected on the unaudited condensed Balance Sheet include the fair value of the interest rate options offset by $0 and $34,970,000 of collateral received from the counterparties at September 30, 2014 and December 31, 2013, respectively.
Schedule of changes in Level 3 assets and liabilities measured at fair value on a recurring basis	'
	Three Months Ended
	September 30, 2014
			Interest rate options
			(dollars in thousands)
	Assets (Liabilities):
	Balance at June 30, 2014	$	18,535
	Total gains or losses (realized/unrealized):
	Included in earnings (or changes in net assets)		(5,425	)
	Balance at September 30, 2014	$	13,110
	Three Months Ended
	September 30, 2013
			Interest rate options
			(dollars in thousands)
	Assets (Liabilities):
	Balance at June 30, 2013	$	43,680
	Total gains or losses (realized/unrealized):
	Included in earnings (or changes in net assets)		(149	)
	Balance at September 30, 2013	$	43,531
	Nine Months Ended
	September 30, 2014
			Interest rate options
			(dollars in thousands)
	Assets (Liabilities):
	Balance at December 31, 2013	$	63,471
	Total gains or losses (realized/unrealized):
	Included in earnings (or changes in net assets)		(50,361	)
	Balance at September 30, 2014	$	13,110
	Nine Months Ended
	September 30, 2013
			Interest rate options
			(dollars in thousands)
	Assets (Liabilities):
	Balance at December 31, 2012	$	25,783
	Total gains or losses (realized/unrealized):
	Included in earnings (or changes in net assets)		17,748
	Balance at September 30, 2013	$	43,531
Schedule of estimated fair values of long term debt, including current maturities	'
	The estimated fair values of our long-term debt, including current maturities at September 30, 2014 and December 31, 2013 were as follows (in thousands):
	2014				2013
			Carrying			Fair		Carrying			Fair
			Value			Value		Value			Value
	Long-term debt	$	7,157,870		$	7,983,009	$	6,954,293		$	7,317,476

Derivative_instruments_Tables

Derivative instruments (Tables)	9 Months Ended
	Sep. 30, 2014
Derivative Instruments	'
Schedule of volume activity of natural gas derivatives that is expected to settle or mature each year	'
	The following table reflects the volume activity of our natural gas derivatives as of September 30, 2014 that is expected to settle or mature each year:
	Year		Natural Gas Swaps
			(MMBTUs)
			(in millions)
	2014		0.4
	2015		7.9
	2016		5.4
	Total		14.3
Schedule of remaining notional amount of forecasted debt issuances hedged in each year with LIBOR swaptions	'
	The following table reflects the remaining notional amount of forecasted debt issuances we have hedged in each year with LIBOR swaptions as of September 30, 2014.
	Year		LIBOR Swaption
			Notional Dollar
			Amount
			(in thousands)
	2014	$	143,629
	2015		470,624
	2016		310,533
	2017		80,169
	Total	$	1,004,955
Schedule of fair value of derivative instruments and their effect on condensed balance sheets	'
	The table below reflects the fair value of derivative instruments and their effect on our condensed balance sheets at September 30, 2014 and December 31, 2013.
		Balance Sheet			Fair Value
		Location
					2014			2013
					(dollars in thousands)
	Not designated as hedges:
	Assets:
	Interest rate options(1)	Other deferred charges		$	13,110		$	63,471
	Natural gas swaps	Other current assets		$	258		$	1,011
	Liabilities:
	Natural gas swaps	Other current liabilities		$	2,022		$	—
	(1)Excludes liability associated with cash collateral of $0 and $34,970,000 as of September 30, 2014 and December 31, 2013, respectively, which is recorded as an offset to the fair value of the swaptions on the unaudited condensed balance sheets.
Schedule of the gross realized gains and (losses) on derivative instruments recognized in margin	'
	The following table presents the gross realized gains and (losses) on derivative instruments recognized in margin for the three and nine months ended September 30, 2014 and 2013.
		Statement of			Three months ended						Nine months ended
		Revenues and			September 30,						September 30,
		Expenses
		Location			2014			2013			2014			2013
					(dollars in thousands)
	Not Designated as hedges:
	Natural Gas Swaps	Fuel			638			122			1,874			688
				$			$			$			$
	Natural Gas Swaps	Fuel			(889	)		(3,089	)		(890	)		(4,002	)
				$	(251	)	$	(2,967	)	$	984		$	(3,314	)
Schedule of gross unrealized gains and (losses) on derivative instruments deferred on the balance sheet	'
	The following table presents the unrealized gains and (losses) on derivative instruments deferred on the balance sheet at September 30, 2014 and December 31, 2013.
		Balance Sheet			2014			2013
		Location
					(dollars in thousands)
	Not designated as hedges:
	Natural gas swaps	Regulatory liability						1,011
				$	—		$
	Natural gas swaps	Regulatory asset		$	(1,764	)	$	—
	Interest rate options	Regulatory asset			(47,598	)		(15,003	)
				$	(49,362	)	$	(13,992	)
Schedule of gross amounts of derivatives and their related offset amounts as permitted by their respective master netting agreements and obligation to return cash collateral	'
	Gross Amounts	Gross	Cash	Net Amounts of
	of Recognized	Amounts	Collateral	Assets Presented on
	Assets	offset on the		the Balance Sheet
	(Liabilities)	Balance Sheet
			(dollars in thousands)
	September 30, 2014
	Assets:
	Natural gas swaps	$	261		$	(2,025	)	$	—		$	(1,764	)
	Interest rate options	$	13,110		$	—		$	—		$	13,110
	December 31, 2013
	Assets:
	Natural gas swaps	$	1,069		$	(58	)	$	—		$	1,011
	Interest rate options	$	63,471		$	—		$	(34,970	)	$	28,501

Investments_in_Debt_and_Equity1

Investments in Debt and Equity Securities (Tables)	9 Months Ended
	Sep. 30, 2014
Investments in Debt and Equity Securities	'
Summary of activities for available-for-sale securities	'
	Gross Unrealized
			(dollars in thousands)
	September 30, 2014		Cost		Gains		Losses			Fair
										Value
	Equity	$	196,523	$	64,560	$	(2,185	)	$	258,898
	Debt		166,710		9,159		(8,417	)		167,452
	Other		13,173		—		(2	)		13,171
	Total	$	376,406	$	73,719	$	(10,604	)	$	439,521
	Gross Unrealized
			(dollars in thousands)
	December 31, 2013		Cost		Gains		Losses			Fair
										Value
	Equity	$	182,755	$	68,424	$	(1,053	)	$	250,126
	Debt		164,941		7,319		(9,070	)		163,190
	Other		12,101		2		—			12,103
	Total	$	359,797	$	75,745	$	(10,123	)	$	425,419

Accumulated_Comprehensive_Marg1

Accumulated Comprehensive Margin (Deficit) (Tables)	9 Months Ended
	Sep. 30, 2014
Accumulated Comprehensive Margin (Deficit)	'
Schedule of changes in accumulated other comprehensive margin (deficit)	'
		Accumulated Other
		Comprehensive Margin
		(Deficit)
		Three Months Ended
			(dollars in thousands)
			Available-for-sale Securities
	Balance at June 30, 2013	$	(399	)
	Unrealized gain		181
	Loss reclassified to net margin		24
	Balance at September 30, 2013	$	(194	)
	Balance at June 30, 2014		278
		$
	Unrealized (loss)		(100
				)
	(Gain) reclassified to net margin		(18
				)
	Balance at September 30, 2014	$	160
		Nine Months Ended
			(dollars in thousands)
			Available-for-sale
			Securities
	Balance at December 31, 2012	$	903
	Unrealized (loss)		(1,041
				)
	(Gain) reclassified to net margin		(56
				)
	Balance at September 30, 2013	$	(194	)
	Balance at December 31, 2013		(549
		$		)
	Unrealized gain		782
	(Gain) reclassified to net margin		(73
				)
	Balance at September 30, 2014	$	160

Regulatory_Assets_and_Liabilit1

Regulatory Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2014
Regulatory Assets and Liabilities	'
Schedule of regulatory assets and liabilities	'
	The following regulatory assets and liabilities are reflected on the unaudited condensed balance sheet as of September 30, 2014 and December 31, 2013.
			2014		2013
			(dollars in thousands)
	Regulatory Assets:
	Premium and loss on reacquired debt(a)	$	74,415	$	82,499
	Amortization on capital leases(b)		11,897		16,124
	Outage costs(c)		44,911		35,155
	Interest rate swap termination fees(d)		10,343		13,336
	Depreciation expense(f)		47,294		48,362
	Deferred charges related to Vogtle Units No. 3 and No. 4 training costs(g)		31,126		27,678
	Interest rate options cost(h)		89,781		38,984
	Deferral of effects on net margin—Smith Energy Facility(i)		96,811		63,491
	Other regulatory assets(j)		5,878		5,479
	Total Regulatory Assets	$	412,456	$	331,108
	Regulatory Liabilities:
	Accumulated retirement costs for other obligations(e)	$	21,069	$	24,520
	Deferral of effects on net margin—Hawk Road Energy Facility(i)		28,605		23,379
	Major maintenance reserve(k)		26,762		28,064
	Deferred debt service adder(l)		64,375		57,223
	Asset retirement obligations(e)		21,508		19,508
	Other regulatory liabilities(j)		4,931		6,095
	Total Regulatory Liabilities	$	167,250	$	158,789
	Net Regulatory Assets		245,206		172,319
		$		$
	(a)Represents premiums paid, together with unamortized transaction costs related to reacquired debt that are being amortized over the lives of the refunding debt, which range up to 30 years.
	(b)Represents the difference between lease payments and the aggregate of the amortization on the capital lease assets and the interest on the capital lease obligations for rate-making purposes. Recovered over the remaining terms of the leases through 2031.
	(c)Consists of both coal-fired maintenance and nuclear refueling outage costs. Coal-fired outage costs are amortized on a straight-line basis to expense over an 18 to 36-month period. Nuclear refueling outage costs are amortized on a straight-line basis to expense over the 18 to 24-month operating cycles of each unit.
	(d)Represents losses on settled interest rate swap arrangements that are being amortized through 2016 and 2019.
	(e)Represents difference in timing of recognition of the costs of decommissioning for financial statement purposes and for ratemaking purposes.
	(f)Prior to Nuclear Regulatory Commission (NRC) approval of a 20-year license extension for Plant Vogtle, we deferred the difference between Plant Vogtle depreciation expense based on the then 40-year operating license and depreciation expense assuming an expected 20-year license extension. Amortization commenced upon NRC approval of the license extension in 2009 and is being amortized over the remaining life of the plant.
	(g)Deferred charges related to Vogtle Units No. 3 and No. 4 training and interest related carrying costs of such training. Amortization will commence effective with the commercial operation date of each unit and amortized to expense over the life of the units.
	(h)Deferral of net loss associated with the change in fair value of the interest rate options to hedge interest rates on certain borrowings related to Vogtle Units No. 3 and No. 4 construction. Amortization will commence in February 2020 and will be amortized through February 2044, the life of the DOE-guaranteed loan which is financing a portion of the construction project.
	(i)Effects on net margin for Smith and Hawk Road Energy Facilities are deferred until the end of 2015 and will be amortized over the remaining life of each respective plant.
	(j)The amortization period for other regulatory assets range up to 35 years and the amortization period of other regulatory liabilities range up to 18 years.
	(k)Represents collections for future major maintenance costs; revenues are recognized as major maintenance costs are incurred.
	(l)Represents collections to fund certain debt payments through the end of 2025 in excess of amounts collected through depreciation expense; the deferred credits will be amortized over the remaining useful life of the plants.

General_Details

General (Details)	9 Months Ended
	Sep. 30, 2014
	item
General	'
Number of electric distribution cooperative members	38

Fair_Value_Details

Fair Value (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Fair value measurement	'	'
Long-term investments	$83,689,000	$81,720,000
Interest rate options	'	'
Fair value measurement	'	'
Derivative assets	13,110,000	63,471,000
Collateral received from counterparties against which fair value of derivative instruments offset	0	34,970,000
Natural gas swaps	'	'
Fair value measurement	'	'
Derivative Liabilities	-1,764,000	'
Derivative assets	'	1,011,000
International equity trust	'	'
Fair value measurement	'	'
Unfunded commitments	0	'
Recurring basis | Total Fair Value | Interest rate options	'	'
Fair value measurement	'	'
Derivative assets	13,110,000	63,471,000
Recurring basis | Total Fair Value | Natural gas swaps	'	'
Fair value measurement	'	'
Derivative Liabilities	-1,764,000	'
Derivative assets	'	1,011,000
Recurring basis | Total Fair Value | Domestic equity	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	151,485,000	143,929,000
Recurring basis | Total Fair Value | International equity trust	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	72,518,000	72,466,000
Long-term investments	11,166,000	11,148,000
Recurring basis | Total Fair Value | Corporate bonds	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	39,713,000	39,863,000
Long-term investments	6,558,000	6,487,000
Recurring basis | Total Fair Value | US Treasury and government agency securities	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	62,440,000	44,846,000
Long-term investments	13,933,000	8,563,000
Recurring basis | Total Fair Value | Agency mortgage and asset backed securities	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	16,736,000	30,133,000
Long-term investments	570,000	3,679,000
Recurring basis | Total Fair Value | Municipal Bonds	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	'	641,000
Recurring basis | Total Fair Value | Other	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	12,940,000	11,820,000
Long-term investments	417,000	284,000
Recurring basis | Total Fair Value | Mutual funds	'	'
Fair value measurement	'	'
Long-term investments	51,045,000	51,559,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	151,485,000	143,929,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | US Treasury and government agency securities	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	62,440,000	44,846,000
Long-term investments	13,933,000	8,563,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	12,940,000	11,820,000
Long-term investments	417,000	284,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds	'	'
Fair value measurement	'	'
Long-term investments	51,045,000	51,559,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Natural gas swaps	'	'
Fair value measurement	'	'
Derivative Liabilities	-1,764,000	'
Derivative assets	'	1,011,000
Recurring basis | Significant Other Observable Inputs (Level 2) | International equity trust	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	72,518,000	72,466,000
Long-term investments	11,166,000	11,148,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate bonds	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	39,713,000	39,863,000
Long-term investments	6,558,000	6,487,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Agency mortgage and asset backed securities	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	16,736,000	30,133,000
Long-term investments	570,000	3,679,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Municipal Bonds	'	'
Fair value measurement	'	'
Nuclear decommissioning trust funds	'	641,000
Recurring basis | Significant Unobservable Inputs (Level 3) | Interest rate options	'	'
Fair value measurement	'	'
Derivative assets	$13,110,000	$63,471,000

Fair_Value_Details_2

Fair Value (Details 2) (Interest Rate Contract Assets And Liabilities Net [Member], USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest Rate Contract Assets And Liabilities Net [Member]	'	'	'	'
Assets (Liabilities):	'	'	'	'
Balance at the beginning of the period	$18,535	$43,680	$63,471	$25,783
Total gains or losses (realized/unrealized):	'	'	'	'
Included in earnings (or changes in net assets)	-5,425	-149	-50,361	17,748
Balance at the end of the period	$13,110	$43,531	$13,110	$43,531

Fair_Value_Details_3

Fair Value (Details 3) (USD $)	Sep. 30, 2014	Sep. 30, 2013
In Thousands, unless otherwise specified
Carrying Reported Amount Fair Value Disclosure [Member]	'	'
Grouping Financial Statement Captions	'	'
Long-term debt	$7,157,870	$6,954,293
Total Fair Value	'	'
Grouping Financial Statement Captions	'	'
Long-term debt	$7,983,009	$7,317,476

Derivative_instruments_Details

Derivative instruments (Details) (Natural gas swaps, USD $)	Sep. 30, 2014	Dec. 31, 2013
	item
Gas hedges	'	'
Derivative Liabilities	($1,764,000)	'
Derivative assets	'	1,011,000
Derivative volume activity that is expected to settle or mature each year (in MMBTUs)	14,300,000	'
Letters of credit required to be posted with counterparties, if credit-risk-related contingent features were triggered due to credit rating being downgraded below investment grade	$2,022,000	'
2014	'	'
Gas hedges	'	'
Derivative volume activity that is expected to settle or mature each year (in MMBTUs)	400,000	'
2015	'	'
Gas hedges	'	'
Derivative volume activity that is expected to settle or mature each year (in MMBTUs)	7,900,000	'
2016	'	'
Gas hedges	'	'
Derivative volume activity that is expected to settle or mature each year (in MMBTUs)	5,400,000	'

Derivative_instruments_Details1

Derivative instruments (Details 2) (Interest rate options, USD $)	3 Months Ended	9 Months Ended
	Dec. 31, 2011	Sep. 30, 2014	Dec. 31, 2013
	item
Derivative instruments and hedging activities	'	'	'
Purchased amount of derivative instrument	$100,000,000	'	'
Variable rate basis	'	'LIBOR	'
Notional Dollar Amount	2,200,000,000	1,004,955,000	'
Number of nuclear units expected to be financed	2	'	'
Derivative notional amount expired	'	1,174,248,000	'
Derivative remaining notional amount	'	1,004,955,000	'
Cash settlement value, if swap rates are at or below the specified fixed rate on the expiration date	'	0	'
Weighted average fixed rate (as a percent)	'	4.08%	'
Notional amount of derivatives, expired without value	'	419,796,000	'
Additional premium payment obligations on interest rate option transactions	'	0	'
Fair value of assets	'	13,110,000	63,471,000
Funds posted as collateral by the counterparties	'	0	34,970,000
Carrying amount of derivative assets	'	13,110,000	28,501,000
2014	'	'	'
Derivative instruments and hedging activities	'	'	'
Notional Dollar Amount	'	143,629,000	'
2015	'	'	'
Derivative instruments and hedging activities	'	'	'
Notional Dollar Amount	'	470,624,000	'
2016	'	'	'
Derivative instruments and hedging activities	'	'	'
Notional Dollar Amount	'	310,533,000	'
2017	'	'	'
Derivative instruments and hedging activities	'	'	'
Notional Dollar Amount	'	80,169,000	'
Minimum	'	'	'
Derivative instruments and hedging activities	'	'	'
Collateral thresholds range	'	0	'
Maximum	'	'	'
Derivative instruments and hedging activities	'	'	'
Collateral thresholds range	'	$10,000,000	'
Average	'	'	'
Derivative instruments and hedging activities	'	'	'
Fixed interest rates above current LIBOR swap rates (as a percent)	'	1.07%	'

Derivative_instruments_Details2

Derivative instruments (Details 3) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Interest rate options	'	'
Assets:	'	'
Fair value of assets	$13,110,000	$63,471,000
Natural gas swaps	'	'
Assets:	'	'
Fair value of assets	'	1,011,000
Liabilities:	'	'
Fair Value of liabilities	1,764,000	'
Liability associated with cash collateral, which is recorded as an offset to the fair value of derivatives	1,764,000	'
Not designated as hedges | Interest rate options	'	'
Assets:	'	'
Fair value of assets	13,110,000	63,471,000
Liabilities:	'	'
Liability associated with cash collateral, which is recorded as an offset to the fair value of derivatives	0	34,970,000
Not designated as hedges | Natural gas swaps	'	'
Assets:	'	'
Fair value of assets	258,000	1,011,000
Liabilities:	'	'
Fair Value of liabilities	$2,022,000	'

Derivative_instruments_Details3

Derivative instruments (Details 4) (Not designated as hedges, USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified			Natural gas swaps	Natural gas swaps	Natural gas swaps	Natural gas swaps	Natural gas swaps	Natural gas swaps	Interest rate options	Interest rate options
			Regulatory Asset	Regulatory Liability	Fuel	Fuel	Fuel	Fuel	Regulatory Asset	Regulatory Asset
Effect of Derivative Instruments on the Condensed Statement of Revenues and Expenses or Balance Sheet	'	'	'	'	'	'	'	'	'	'
Gains	'	'	'	'	$638	$122	$1,874	$688	'	'
Losses	'	'	'	'	-889	-3,089	-890	-4,002	'	'
Total gains (losses) on derivatives	'	'	'	'	-251	-2,967	984	-3,314	'	'
Unrealized losses on derivatives	'	'	-1,764	'	'	'	'	'	-47,598	-15,003
Unrealized gains on derivatives	'	'	'	1,011	'	'	'	'	'	'
Unrealized gains and (losses) on derivatives	($49,362)	($13,992)	'	'	'	'	'	'	'	'

Derivative_instruments_Details4

Derivative instruments (Details 5) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Natural gas swaps	'	'
Assets:	'	'
Gross Amounts of Recognized Assets (Liabilities)	$261,000	$1,069,000
Gross Amounts offset on the Balance Sheet	-2,025,000	-58,000
Net Amounts of Assets Presented on the Balance Sheet	-1,764,000	'
Net Amounts of Assets Presented on the Balance Sheet	'	1,011,000
Interest rate options	'	'
Assets:	'	'
Gross Amounts of Recognized Assets (Liabilities)	13,110,000	63,471,000
Cash Collateral	'	-34,970,000
Net Amounts of Assets Presented on the Balance Sheet	$13,110,000	$28,501,000

Investments_in_Debt_and_Equity2

Investments in Debt and Equity Securities (Details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investments in Debt and Equity Securities	'	'
Available-for-sale securities, gross unrealized losses that were in effect for less than one year (as a percent)	79.00%	'
Available-for-sale securities	'	'
Cost	$376,406	$359,797
Gross Unrealized Gains	73,719	75,745
Gross Unrealized Losses	-10,604	-10,123
Fair Value	439,521	425,419
Equity	'	'
Available-for-sale securities	'	'
Cost	196,523	182,755
Gross Unrealized Gains	64,560	68,424
Gross Unrealized Losses	-2,185	-1,053
Fair Value	258,898	250,126
Debt	'	'
Available-for-sale securities	'	'
Cost	166,710	164,941
Gross Unrealized Gains	9,159	7,319
Gross Unrealized Losses	-8,417	-9,070
Fair Value	167,452	163,190
Other	'	'
Available-for-sale securities	'	'
Cost	13,173	12,101
Gross Unrealized Gains	'	2
Gross Unrealized Losses	-2	'
Fair Value	$13,171	$12,103

Accumulated_Comprehensive_Marg2

Accumulated Comprehensive Margin (Deficit) (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Comprehensive Margin (Deficit)	'	'	'	'
Effective income tax rate (as a percent)	'	'	0.00%	'
Accumulated other comprehensive margin (deficit)	'	'	'	'
Balance at the beginning of the period	$278	($399)	($549)	$903
Unrealized gain (loss)	-100	181	782	-1,041
Loss (Gain) reclassified to net margin	-18	24	-73	-56
Balance at the end of the period	$160	($194)	$160	($194)

Contingencies_and_Regulatory_M1

Contingencies and Regulatory Matters (Details) (USD $)	9 Months Ended	1 Months Ended		0 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Apr. 30, 2008	Sep. 30, 2014	Aug. 20, 2014	Jul. 28, 2014	Jul. 28, 2014
	item	Vogtle Units Number3 And Number4	Costs Associated With Design Changes Delays In Project Schedule And Issuance Of Combined Construction Permits And Operating Licenses	Patronage Capital Litigation	Patronage Capital Litigation	Patronage Capital Litigation
		item	Vogtle Units Number3 And Number4	item	item	Maximum
		MW
Nuclear Construction	'	'	'	'	'	'
Number of Westinghouse AP1000 nuclear generating units	'	2	'	'	'	'
Nominally rated generating capacity for each unit	'	1,100	'	'	'	'
Contractor's estimated adjustment attributable to the entity	'	'	$280	'	'	'
Number of defendant members	'	'	'	2	3	'
Number of excluded members against whom defendant class action is certified	'	'	'	'	1	'
Number of electric distribution cooperative members	38	'	'	'	38	'
Number of former consumer members	'	'	'	'	4	'
Number of members in which the former consumer members filing the lawsuit belonged	'	'	'	'	4	'
Percentage of cooperatives total booked patronage capital	'	'	'	'	30.00%	'
Period of revolving schedule to retire the patronage capital of former consumer-members	'	'	'	'	'	'13 years
Period of revolving schedule to adopt policies to periodically retire the patronage capital of all consumer-members	'	'	'	'	'	'13 years
Number of current consumer members	'	'	'	2	'	'
Number of plaintiffs' classes	'	'	'	3	'	'

Recovered_Sheet1

Restricted Cash and Investments (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Restricted Short-term Investments	'	'
Restricted Cash and Investments	$344,131,000	$307,661,000
Restricted Cash and Investments, Noncurrent	$96,432,000	$34,975,000
Guaranteed interest rate on deposit with Rural Utilities Service (as a percent)	5.00%	5.00%

Regulatory_Assets_and_Liabilit2

Regulatory Assets and Liabilities (Details) (USD $)

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

In Thousands, unless otherwise specified

Accumulated Retirement Costs Other Obligation [Member]

Accumulated Retirement Costs Other Obligation [Member]

Deferred Effects On Net Margin For Energy Facilities [Member]

Deferred Effects On Net Margin For Energy Facilities [Member]

Major Maintenance Sinking Fund [Member]

Major Maintenance Sinking Fund [Member]

Deferred Debt Service Adder [Member]

Deferred Debt Service Adder [Member]

Asset Retirement Obligation Costs [Member]

Asset Retirement Obligation Costs [Member]

Other Regulatory Liabilities [Member]

Other Regulatory Liabilities [Member]

Other Regulatory Liabilities [Member]

Premium And Loss On Reacquired Debt [Member]

Premium And Loss On Reacquired Debt [Member]

Premium And Loss On Reacquired Debt [Member]

Amortization Of Capital Leases [Member]

Amortization Of Capital Leases [Member]

Unamortized Deferred Outage Costs Net [Member]

Unamortized Deferred Outage Costs Net [Member]

Unamortized Deferred Interest Rate Swap Termination Fees [Member]

Unamortized Deferred Interest Rate Swap Termination Fees [Member]

Unamortized Deferred Depreciation Expense [Member]

Unamortized Deferred Depreciation Expense [Member]

Unamortized Deferred Depreciation Expense [Member]

Deferred Training Costs V3 V4 [Member]

Deferred Training Costs V3 V4 [Member]

Interest Rate Option Cost [Member]

Interest Rate Option Cost [Member]

Deferred Effect On Net Margin For Energy Facilities [Member]

Deferred Effect On Net Margin For Energy Facilities [Member]

Other Regulatory Assets [Member]

Other Regulatory Assets [Member]

Other Regulatory Assets [Member]

Unamortized Deferred Coal Fired Outage Costs Net [Member]

Unamortized Deferred Coal Fired Outage Costs Net [Member]

Unamortized Deferred Nuclear Refueling Outage Costs Net [Member]

Unamortized Deferred Nuclear Refueling Outage Costs Net [Member]

Hawk Road [Member]

Hawk Road [Member]

Maximum

Maximum

Plant Vogtle [Member]

Vogtle Units Number3 And Number4

Vogtle Units Number3 And Number4

Smith [Member]

Smith [Member]

Maximum

Minimum

Maximum

Minimum

Maximum

Regulatory assets and liabilities

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total Regulatory Assets

$412,456

$331,108

'

'

'

'

'

'

'

'

'

'

'

'

'

$74,415

$82,499

'

$11,897

$16,124

$44,911

$35,155

$10,343

$13,336

$47,294

$48,362

'

$31,126

$27,678

$89,781

$38,984

$96,811

$63,491

$5,878

$5,479

'

'

'

'

'

Total Regulatory Liabilities

167,250

158,789

21,069

24,520

28,605

23,379

26,762

28,064

64,375

57,223

21,508

19,508

4,931

6,095

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net Regulatory Assets

$245,206

$172,319

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'30 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'35 years

'18 months

'36 months

'18 months

'24 months

Operating license expected extension period for Plant Vogtle

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'20 years

'

'

'

'

'

'

'

'

'

'

'

'

'

Operating license, expected extension period, for Plant Vogtle

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'40 years

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'18 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt_Details

Debt (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Feb. 20, 2014	Sep. 30, 2014	Feb. 20, 2014	Feb. 20, 2014	Feb. 20, 2014	Feb. 20, 2014	Jun. 12, 2014
			Facility	Facility	Facility	Facility	Term loan	Commercial paper	4.55% first mortgage bonds, Series 2014A
					Minimum	Maximum
Debt	'	'	'	'	'	'	'	'	'
Aggregate borrowings expressed as a percentage of Eligible Project Costs	'	'	'	'	'	70.00%	'	'	'
Aggregate borrowings	'	'	'	'	'	$3,057,069,461	'	'	'
Capitalized interest	'	'	335,471,604	'	'	'	'	'	'
Principal amount	'	'	725,000,000	35,900,000	'	'	'	'	250,000,000
Total investment	4,577,424,000	4,434,728,000	'	'	'	'	'	'	'
Fixed interest rate (as a percent)	'	'	3.87%	'	'	'	'	'	'
Repayment of outstanding debt	'	'	'	'	'	'	260,000,000	465,000,000	'
Term of each advance	'	'	'	'	'3 months	'	'	'	'
Interest accrued and payable through November 20, 2019, is reflected as additional borrowings under the Facility	'	'	'	'	'	335,471,604	'	'	'
Amount of interest reflected as long-term debt on the condensed balance sheet	'	'	'	17,179,000	'	'	'	'	'
Basis spread (as a percent)	'	'	0.38%	'	'	'	'	'	'
Issuance costs	'	'	$51,000,000	'	'	'	'	'	'
Interest rate (as a percent)	'	'	'	'	'	'	'	'	4.55%

Purchase_agreements1

Purchase agreements (Precedent Agreement, Transcontinental Gas Pipeline Company LLC [Member], USD $)	0 Months Ended
	Apr. 11, 2014
Precedent Agreement | Transcontinental Gas Pipeline Company LLC [Member]	'
Purchase Agreements Line Items	'
Base term of an agreement	'25 years
Agreement fixed charge for the base term	$37,700,000