Oglethorpe Power 10-Q 12 Aug 15 2015 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - Jun. 30, 2015 - shares	Total
Document and Entity Information
Entity Registrant Name	OGLETHORPE POWER CORP
Entity Central Index Key	788,816
Document Type	10-Q
Document Period End Date	Jun. 30, 2015
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	2,015
Document Fiscal Period Focus	Q2

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Electric plant:
In service	$ 8,430,496	$ 8,345,241
Less: Accumulated provision for depreciation	(3,837,389)	(3,762,690)
Total in service	4,593,107	4,582,551
Nuclear fuel, at amortized cost	360,297	369,529
Construction work in progress	2,507,335	2,374,392
Total electric plant	7,460,739	7,326,472
Investments and funds:
Nuclear decommissioning trust fund	373,236	366,004
Investment in associated companies	68,230	67,368
Long-term investments	84,833	85,728
Restricted cash and investments	76,535	118,390
Other	18,316	17,397
Total investments and funds	621,150	654,887
Current assets:
Cash and cash equivalents	286,777	237,391
Restricted short-term investments	252,652	247,057
Receivables	141,537	130,366
Inventories, at average cost	267,992	270,849
Prepayments and other current assets	23,260	12,667
Total current assets	972,218	898,330
Deferred charges:
Deferred debt expense, being amortized	97,553	97,902
Regulatory assets	513,026	484,049
Prepayments to Georgia Power Company	80,580	73,726
Other	11,750	10,877
Total deferred charges	702,909	666,554
Total assets	9,757,016	9,546,243
Capitalization:
Patronage capital and membership fees	787,345	761,124
Accumulated other comprehensive margin	107	468
Total patronage capital and membership fees and accumulated other comprehensive margin	787,452	761,592
Long-term debt	7,326,478	7,113,000
Obligation under capital leases	98,532	100,456
Other	16,988	16,434
Total capitalization	8,229,450	7,991,482
Current liabilities:
Long-term debt and capital leases due within one year	161,294	160,754
Short-term borrowings	261,744	234,369
Accounts payable	42,924	98,337
Accrued interest	58,792	58,841
Member power bill prepayments, current	143,681	166,013
Other current liabilities	54,619	70,748
Total current liabilities	723,054	789,062
Deferred credits and other liabilities:
Gain on sale of plant, being amortized	19,936	20,676
Asset retirement obligations	465,573	432,260
Member power bill prepayments, non-current	43,240	31,941
Power sale agreement, being amortized	6,334	12,669
Regulatory liabilities	192,970	194,073
Other	76,459	74,080
Total deferred credits and other liabilities	804,512	765,699
Total equity and liabilities	$ 9,757,016	$ 9,546,243

Consolidated Statements of Reve

Consolidated Statements of Revenues and Expenses - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Operating revenues:
Sales to Members	$ 311,148	$ 338,116	$ 619,924	$ 672,875
Sales to non-Members	32,593	17,867	63,595	50,408
Total operating revenues	343,741	355,983	683,519	723,283
Operating expenses:
Fuel	115,211	133,976	223,620	266,252
Production	128,369	99,004	243,128	207,088
Depreciation and amortization	42,952	41,404	85,604	82,118
Purchased power	14,612	16,312	28,243	36,378
Accretion	6,477	6,108	12,859	12,126
Deferral of Hawk Road and Smith Energy Facilities effect on net margin	(27,374)	(10,421)	(41,689)	(20,136)
Total operating expenses	280,247	286,383	551,765	583,826
Operating margin	63,494	69,600	131,754	139,457
Other income:
Investment income	10,185	9,145	20,034	18,427
Amortization of deferred gains	370	447	740	894
Allowance for equity used during construction	168	342	342	731
Other	1,903	1,443	4,218	2,984
Total other income	12,626	11,377	25,334	23,036
Interest charges:
Interest expense	88,132	85,965	175,839	167,882
Allowance for debt funds used during construction	(26,699)	(26,385)	(52,952)	(50,114)
Amortization of debt discount and expense	3,835	4,201	7,980	8,306
Net interest charges	65,268	63,781	130,867	126,074
Net margin	$ 10,852	$ 17,196	$ 26,221	$ 36,419

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Margin - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Consolidated Statements of Comprehensive Margin
Net margin	$ 10,852	$ 17,196	$ 26,221	$ 36,419
Other comprehensive margin:
Unrealized (loss) gain on available-for-sale securities	(314)	431	(361)	827
Total comprehensive margin	$ 10,538	$ 17,627	$ 25,860	$ 37,246

Consolidated Statements of Patr

Consolidated Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive Margin (Deficit) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Increase (Decrease) in Members' Capital
Balance			$ 761,592	$ 713,940
Components of comprehensive margin:
Net margin	$ 10,852	$ 17,196	26,221	36,419
Unrealized (loss) gain on available-for-sale securities	(314)	431	(361)	827
Balance	787,452	751,186	787,452	751,186
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance			761,124	714,489
Components of comprehensive margin:
Net margin			26,221	36,419
Balance	787,345	750,908	787,345	750,908
Accumulated Other Comprehensive Margin (Deficit)
Increase (Decrease) in Members' Capital
Balance			468	(549)
Components of comprehensive margin:
Unrealized (loss) gain on available-for-sale securities			(361)	827
Balance	$ 107	$ 278	$ 107	$ 278

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net margin	$ 26,221	$ 36,419
Adjustments to reconcile net margin to net cash provided by operating activities:
Depreciation and amortization, including nuclear fuel	156,416	153,759
Accretion cost	12,859	12,126
Amortization of deferred gains	(894)	(894)
Allowance for equity funds used during construction	(342)	(731)
Deferred outage costs	(18,274)	(31,411)
Deferral of Hawk Road and Smith Energy Facilities effect on net margin	(41,689)	(20,136)
Gain on sale of investments	(32,470)	(8,961)
Regulatory deferral of costs associated with nuclear decommissioning	25,781	1,571
Other	13,216	6,816
Change in operating assets and liabilities:
Receivables	(11,171)	(21,180)
Inventories	2,857	32,455
Prepayments and other current assets	(10,664)	1,209
Accounts payable	(45,059)	(45,456)
Accrued interest	(49)	183
Accrued taxes	820	(3,978)
Other current liabilities	(8,681)	(2,479)
Member power bill prepayments	(11,033)	14,475
Total adjustments	31,623	87,368
Net cash provided by operating activities	57,844	123,787
Cash flows from investing activities:
Property additions	(256,038)	(249,317)
Activity in nuclear decommissioning trust fund - Purchases	(281,938)	(188,815)
Activity in nuclear decommissioning trust fund - Proceeds	279,751	186,165
Decrease in restricted cash and investments	41,855	32,209
Increase in restricted short-term investments	(5,524)	(21,173)
Activity in other long-term investments - Purchases	(23,746)	(28,690)
Activity in other long-term investments - Proceeds	24,973	30,385
Activity on interest rate options - Collateral returned		(73,850)
Activity on interest rate options - Collateral received		41,640
Other	(8,450)	473
Net cash used in investing activities	(229,117)	(270,973)
Cash flows from financing activities:
Long-term debt proceeds	271,892	993,707
Long-term debt payments	(76,418)	(333,127)
Increase (decrease) in short-term borrowings, net	27,375	(548,494)
Other	(2,190)	(43,227)
Net cash provided by financing activities	220,659	68,859
Net increase (decrease) in cash and cash equivalents	49,386	(78,327)
Cash and cash equivalents at beginning of period	237,391	408,193
Cash and cash equivalents at end of period	286,777	329,866
Cash paid for -
Interest (net of amounts capitalized)	127,026	115,231
Supplemental disclosure of non-cash investing and financing activities:
Change in plant expenditures included in accounts payable	$ (8,454)	$ 22,904

General

General	6 Months Ended
	Jun. 30, 2015
General
General	(A) General. The consolidated 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- month and six-month periods ended June 30, 2015 and 2014. 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. These consolidated 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, 2014, as filed with the SEC. The results of operations for the three-month and six-month periods ended June 30, 2015 are not necessarily indicative of results to be expected for the full year. As noted in our 2014 Form 10-K, our revenues consist primarily of sales to our 38 electric distribution cooperative members and, thus, the receivables on the consolidated balance sheets are principally from our members. (See "Notes to Financial Statements" in our 2014 Form 10-K.)

Fair Value

Fair Value	6 Months Ended
	Jun. 30, 2015
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 June 30, 2015 and December 31, 2014. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at Reporting Date Using June 30, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) Nuclear decommissioning trust funds: Domestic equity $ $ $ — $ — International equity trust — — Corporate bonds — — US Treasury and government agency securities — — Agency mortgage and asset backed securities — — Municipal bonds — — Other — — Long-term investments: International equity trust — — Corporate bonds — — US Treasury and government agency securities — — Agency mortgage and asset backed securities — — Mutual funds — — Other — — Interest rate options — — Natural gas swaps — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at Reporting Date Using December 31, 2014 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) Nuclear decommissioning trust funds: Domestic equity $ $ $ — $ — International equity trust — — Corporate bonds — — US Treasury and government agency securities — — Agency mortgage and asset backed securities — — Municipal Bonds — — Other — — Long-term investments: Corporate bonds — — US Treasury and government agency securities — — Agency mortgage and asset backed securities — — International equity trust — — Mutual funds — — Other — — Interest rate options — — Natural gas swaps — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 six months ended June 30, 2015 and 2014. ​ ​ ​ ​ ​ Three Months Ended June 30, 2015 ​ ​ ​ ​ ​ Interest rate options ​ ​ ​ ​ ​ (dollars in thousands) Assets (Liabilities): Balance at March 31, 2015 $ Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) ​ ​ ​ ​ ​ Balance at June 30, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, 2014 ​ ​ ​ ​ ​ Interest rate options ​ ​ ​ ​ ​ (dollars in thousands) Assets (Liabilities): Balance at March 31, 2014 $ Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) ) ​ ​ ​ ​ ​ Balance at June 30, 2014 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended June 30, 2015 ​ ​ ​ ​ ​ Interest rate options ​ ​ ​ ​ ​ (dollars in thousands) Assets (Liabilities): Balance at December 31, 2014 $ Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) ​ ​ ​ ​ ​ Balance at June 30, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended June 30, 2014 ​ ​ ​ ​ ​ Interest rate options ​ ​ ​ ​ ​ (dollars in thousands) Assets (Liabilities): Balance at December 31, 2013 $ Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) ) ​ ​ ​ ​ ​ Balance at June 30, 2014 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 June 30, 2015 and December 31, 2014 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2015 2014 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Carrying Value Fair Value Carrying Value Fair Value ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Long-term debt $ $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 data provider, 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 June 30, 2015 plus an applicable spread, which reflects our borrowing rate for new loans of this type from the Federal Financing Bank. The rates on the CFC debt are fixed and the valuation is based on rate quotes provided by CFC. We use an interest rate quote sheet provided by CoBank for valuation of the CoBank debt, which reflects current rates for a similar loan. 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	6 Months Ended
	Jun. 30, 2015
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 June 30, 2015, 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 June 30, 2015 and December 31, 2014, the fair value of our natural gas contracts was a net liability of approximately $15,942,000 and $18,914,000, respectively. As of June 30, 2015 and December 31, 2014, 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 June 30, 2015 due to our credit rating being downgraded below investment grade, we would have been required to post letters of credit in the amount of $16,158,000 with our counterparties. The following table reflects the volume activity of our natural gas derivatives as of June 30, 2015 that is expected to settle or mature each year: ​ ​ ​ ​ ​ Year Natural Gas Swaps (MMBTUs) (in millions) ​ ​ ​ ​ ​ 2015 2016 2017 ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​ Interest rate options. We are exposed to the risk of rising interest rates due to the significant amount of new long-term debt we expect to incur in connection with anticipated capital expenditures, particularly the construction of Vogtle Units No. 3 and No. 4. In 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 the two additional nuclear units at Plant Vogtle. Since inception, swaptions having a notional amount of approximately $1,549,683,000 have expired and as of June 30, 2015 the remaining notional amount of our outstanding swaptions was approximately $629,520,000. 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 127 basis points above the corresponding LIBOR swap rates that were in effect as of June 30, 2015, and the weighted average fixed rate is 3.98%. Swaptions having notional amounts totaling $231,806,000 expired without value during the six months ended June 30, 2015. 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. At June 30, 2015 and December 31, 2014, the fair value of these swaptions was approximately $4,715,000 and $4,371,000, 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 June 30, 2015 and December 31, 2014, there were no collateral postings made by the counterparties, 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 $2,200,000,000 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 June 30, 2015. ​ ​ ​ ​ ​ Year LIBOR Swaption Notional Dollar Amount (in thousands) ​ ​ ​ ​ ​ 2015 $ 2016 2017 ​ ​ ​ ​ ​ Total $ ​ ​ ​ ​ ​ The table below reflects the fair value of derivative instruments and their effect on our consolidated balance sheets at June 30, 2015 and December 31, 2014. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance Sheet Location Fair Value ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2015 2014 (dollars in thousands) Not designated as hedges: Assets: Interest rate options Other deferred charges $ $ Liabilities: Natural gas swaps Other current liabilities $ $ Natural gas swaps Other deferred credits ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The following table presents the gross realized gains and (losses) on derivative instruments recognized in margin for the three and six months ended June 30, 2015 and 2014. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Statement of Revenues and Expenses Three months ended June 30, Six months ended June 30, Location 2015 2014 2015 2014 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) Not Designated as hedges: Natural Gas Swaps Fuel $ $ $ $ Natural Gas Swaps Fuel ) — ) — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ ) $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The following table presents the unrealized gains and (losses) on derivative instruments deferred on the balance sheet at June 30, 2015 and December 31, 2014. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance Sheet Location 2015 2014 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) Not designated as hedges: Natural gas swaps Regulatory asset $ ) $ ) Interest rate options Regulatory asset ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total not designated as hedges $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 of Recognized Assets (Liabilities) Gross Amounts offset on the Balance Sheet Cash Collateral Net Amounts of Assets Presented on the Balance Sheet ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) June 30, 2015 Assets: Natural gas swaps $ ) $ — $ — $ ) Interest rate options $ $ ) $ — $ December 31, 2014 Assets: Natural gas swaps $ ) $ — $ — $ ) Interest rate options $ $ ) $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Investments in Debt and Equity

Investments in Debt and Equity Securities	6 Months Ended
	Jun. 30, 2015
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 June 30, 2015, approximately 61% of these gross unrealized losses had been unrealized for a duration of less than one year. The following tables summarize the activities for available-for-sale securities as of June 30, 2015 and December 31, 2014. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) June 30, 2015 Cost Gains Losses Fair Value ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity $ $ $ ) $ Debt ) Other — ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) December 31, 2014 Cost Gains Losses Fair Value ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity $ $ $ ) $ Debt ) Other — ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Recently Issued or Adopted Acco

Recently Issued or Adopted Accounting Pronouncements	6 Months Ended
	Jun. 30, 2015
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 (FASB) 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 using either of the following transition methods: (i) a full retrospective approach reflecting the application of the standard in each prior reporting period with the option to elect certain practical expedients, or (ii) a modified retrospective approach with the cumulative effect of initially adopting the standard recognized at the date of adoption (which includes additional footnote disclosures). Early adoption is not permitted. On July 9, 2015, the FASB voted to defer the effective date by one year. Under the amendment, the standard would be effective for annual reporting periods beginning after December 15, 2017 and interim periods therein. The amendment also permits early adoption of the standard, but not before the original effective date of December 15, 2016. We are currently evaluating the future impact of this standard to our consolidated financial position or results of operations. In July 2015, the FASB issued "Inventory (Topic 330): Simplifying the Measurement of Inventory." Under the new inventory standard, inventories are required to be measured at the lower of cost and net realizable value, the latter representing the estimated selling price in the ordinary course of business, reduced by costs of completion, disposal, and transportation. Under current guidance, inventories are required to be measured at the lower of cost or market, but depending upon specific circumstances, market could be replacement cost, net realizable value, or net realizable value reduced by a normal profit margin. The amendments do not apply to inventory measured using the last-in, first-out (LIFO) or the retail inventory method. The amendments apply to all other inventory, which includes inventory that is measured using first-in, first out (FIFO) or average cost, the method used to measure all of our inventories. The new standard is effective for us prospectively for annual reporting periods beginning after December 15, 2016, and interim periods therein. Early adoption is permitted as of the beginning of an interim or annual reporting period. We are currently evaluating the future impact of this standard to our consolidated financial position or results of operations. In April 2015, the FASB issued "Interest-Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs". The amendments in this standard require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The amendments in the standard are effective for the financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. We are currently evaluating the impact of adoption on our consolidated financial position or results of operations.

Accumulated Comprehensive Margi

Accumulated Comprehensive Margin (Deficit)	6 Months Ended
	Jun. 30, 2015
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 Consolidated 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 2014 Form 10-K. Amounts reclassified to net margin in the table below are reflected in "Other income" on our unaudited Consolidated Statements 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 June 30, 2014 ​ ​ ​ ​ ​ (dollars in thousands) Available-for-sale Securities ​ ​ ​ ​ ​ Balance at March 31, 2014 $ ) Unrealized gain (Gain) reclassified to net margin ) ​ ​ ​ ​ ​ Balance at June 30, 2014 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, 2015 ​ ​ ​ ​ ​ (dollars in thousands) Available-for-sale Securities ​ ​ ​ ​ ​ Balance at March 31, 2015 $ Unrealized loss ) (Gain) reclassified to net margin ) ​ ​ ​ ​ ​ Balance at June 30, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended June 30, 2014 ​ ​ ​ ​ ​ (dollars in thousands) Available-for-sale Securities ​ ​ ​ ​ ​ Balance at December 31, 2013 $ ) Unrealized gain (Gain) reclassified to net margin ) ​ ​ ​ ​ ​ Balance at June 30, 2014 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended June 30, 2015 ​ ​ ​ ​ ​ (dollars in thousands) Available-for-sale Securities ​ ​ ​ ​ ​ Balance at December 31, 2014 $ Unrealized loss ) (Gain) reclassified to net margin ) ​ ​ ​ ​ ​ Balance at June 30, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Contingencies and Regulatory Ma

Contingencies and Regulatory Matters	6 Months Ended
	Jun. 30, 2015
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 CB&I Stone & Webster, Inc. (formerly known as Stone & Webster, Inc.) (collectively, the Contractor) entered into an engineering, procurement, and construction agreement (the EPC Agreement) to design, engineer, procure, construct and test 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 EPC Agreement for Vogtle Units No. 3 and No. 4, 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. In July 2012, the Co-owners and Contractor began negotiations regarding costs associated with design changes to the Westinghouse AP1000 Design Control Document (DCD) and 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, including the assertion by the Contractor that the Co-owners are responsible for these costs under the terms of the EPC 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 March 2015, the U.S. Court of Appeals for the District of Columbia affirmed the dismissal, which means the case will be tried in the U.S. District Court for the Southern District of Georgia. The portion of the additional costs claimed by the Contractor that would be attributable to us, based on our ownership interest, is approximately $280,000,000 in 2008 dollars, or $390,000,000 in 2015 dollars, with respect to these issues. The Contractor has also asserted that it is entitled to extensions of the guaranteed substantial completion dates of April 2016 and April 2017 for Vogtle Units No. 3 and No. 4, respectively. 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 EPC 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 EPC Agreement. The Contractor did not specify amounts relating to these new allegations in its amended counterclaim; however, the Contractor subsequently asserted estimated minimum damages related to the counterclaim, based on our ownership interest, of approximately $75,000,000 in 2014 dollars, or $78,000,000 in 2015 dollars. In June 2015, the Contractor updated its estimated damages under the initial complaint and the amended counterclaim, to an aggregate, based on our ownership interest, of approximately $470,000,000 in 2015 dollars. The Contractor may from time to time continue to assert that it is entitled to additional payments with respect to these 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. 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 June 30, 2015, 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. 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 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 Investments

Restricted Cash and Investments	6 Months Ended
	Jun. 30, 2015
Restricted Cash and Investments.
Restricted Cash and Investments	(H) Restricted Cash and Investments . Restricted cash and investments primarily consist of 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. At June 30, 2015 and December 31, 2014, we had restricted cash and investments totaling $329,253,000 and $365,585,000, respectively, of which $76,535,000 and $118,390,000, respectively, were classified as long-term.

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	6 Months Ended
	Jun. 30, 2015
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 consolidated balance sheet as of June 30, 2015 and December 31, 2014. ​ ​ ​ ​ ​ ​ ​ ​ 2015 2014 (dollars in thousands) ​ ​ ​ ​ ​ ​ ​ ​ Regulatory Assets: Premium and loss on reacquired debt (a) $ $ Amortization on capital leases (b) Outage costs (c) Interest rate swap termination fees (d) Depreciation expense (e) Deferred charges related to Vogtle Units No. 3 and No. 4 training costs (f) Interest rate options cost (g) Deferral of effects on net margin—Smith Energy Facility (h) Other regulatory assets (m) ​ ​ ​ ​ ​ ​ ​ ​ Total Regulatory Assets $ $ Regulatory Liabilities: Accumulated retirement costs for other obligations (i) $ $ Deferral of effects on net margin—Hawk Road Energy Facility (h) Major maintenance reserve (j) Amortization on capital leases (b) Deferred debt service adder (k) Asset retirement obligations (l) Other regulatory liabilities (m) ​ ​ ​ ​ ​ ​ ​ ​ Total Regulatory Liabilities $ $ ​ ​ ​ ​ ​ ​ ​ ​ Net Regulatory Assets $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (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. (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 a 24-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) 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. (f) 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. (g) Deferral of net loss associated with the change in fair value and expired cost of interest rate options purchased 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. (h) 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. (i) Represents difference in timing of recognition of retirement costs associated with long-lived assets in which there are no legal obligations to retire for financial statement purposes and for ratemaking purposes. (j) Represents collections for future major maintenance costs; revenues are recognized as major maintenance costs are incurred. (k) Represents collections to fund certain debt payments to be made through the end of 2025 which will be in excess of amounts collected through depreciation expense; the deferred credits will be amortized over the remaining useful life of the plants. (l) Represents difference in timing of recognition of the costs of decommissioning for financial statement purposes and for ratemaking purposes. (m) 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.

Member Power Bill Prepayments

Member Power Bill Prepayments	6 Months Ended
	Jun. 30, 2015
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 July 2020, with the majority of the balance scheduled to be credited by the end of 2015.

Debt

Debt	6 Months Ended
	Jun. 30, 2015
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 pursuant to which the Department of Energy agreed to guarantee our obligations 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 two future advance promissory notes, each dated February 20, 2014, made by us to the 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 the 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. Advances may be requested under the Facility on a quarterly basis through December 31, 2020. On June 12, 2015 we received advances under the Facility totaling $145,000,0 00. At June 30, 2015, aggregate borrowings totaled $1,036,135,000, including capitalized interest advanced under the loan. b) Rural Utilities Service Guaranteed Loans: For the six-month period ended June 30, 2015 we received advances on Rural Utilities Service-guaranteed Federal Financing Bank loans totaling $126,892,000 for general and environmental improvements at existing plants. In July 2015, we received an additional $18,018,000 in advances on Rural Utilities Service-guaranteed Federal Financing Bank loans for general and environmental improvements at existing plants. c) Credit Facilities: On March 23, 2015, we entered into a 5-year $1,210,000,000 credit agreement with a syndicate of thirteen lenders, led by the National Rural Utilities Cooperative Finance Corporation as administrative agent.

Nuclear Fuel Disposal Cost Liti

Nuclear Fuel Disposal Cost Litigation	6 Months Ended
	Jun. 30, 2015
Nuclear Fuel Disposal Cost Litigation
Nuclear Fuel Disposal Cost Litigation	(L) Nuclear Fuel Disposal Cost Litigation. Contracts with the U.S. Department of Energy have been executed to provide for the permanent disposal of spent nuclear fuel produced at Plants Hatch and Vogtle. The Department of Energy failed to begin disposing of spent fuel in January 1998 as required by the contracts, and Georgia Power, as agent for the co-owners of the plants, is pursuing legal remedies against the Department of Energy for breach of contract. On December 14, 2014, the U.S. Court of Federal Claims issued a judgment in favor of Georgia Power, as agent for the co-owners, to recover spent nuclear fuel storage costs at Hatch and Vogtle Units No. 1 and No. 2 covering the period of January 1, 2005 through December 31, 2010. Our ownership share of the $36,474,000 total award was $10,949,000, which was received in April 2015. The effects of the award were recorded during the first quarter of 2015 and resulted in a $7,320,000 reduction in total operating expenses, including reductions to fuel expense and production costs, as well as a $3,629,000 reduction to plant in service.

Asset Retirement Obligations

Asset Retirement Obligations	6 Months Ended
	Jun. 30, 2015
Asset Retirement Obligation Disclosure
Asset Retirement Obligations	(M) Asset Retirement Obligations. Asset retirement obligations are legal obligations associated with the retirement of long-lived assets. These obligations represent the present value of the estimated costs for an asset's future retirement and are recorded in the period in which the liability is incurred. The liabilities we have recognized primarily relate to the decommissioning of our nuclear facilities. In addition, we have retirement obligations related to ash ponds, gypsum, landfill sites and asbestos removal. Under the accounting provision for regulated operations, we record a regulatory asset or liability to reflect the difference in timing of recognition of the costs related to nuclear and coal ash related decommissioning for financial statement purposes and for ratemaking purposes. On April 17, 2015 EPA published its final coal combustion residuals (CCR) rule which regulates CCRs as non-hazardous materials under Subtitle D of the Resource Conservation and Recovery Act. The rule takes effect on October 19, 2015. Based on a preliminary assessment of the impact of the final CCR rule, we revised the forecasted cash flows related to the existing asset retirement obligations and increased the obligations and corresponding assets in electric plant in service by approximately $20,711,000 in the second quarter of 2015. The liabilities are estimates based on various assumptions including, but not limited to, closure and post-closure cost estimates, timing of expenditures, escalation factors, discount rates and methods for complying with the CCR rule. Additional adjustments to the asset retirement obligations are expected periodically as we continue to assess the impact of the rule on our estimates and assumptions.

Fair Value (Tables)

Fair Value (Tables)	6 Months Ended
	Jun. 30, 2015
Fair Value
Schedule of assets and liabilities measured at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at Reporting Date Using June 30, 2015 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) Nuclear decommissioning trust funds: Domestic equity $ $ $ — $ — International equity trust — — Corporate bonds — — US Treasury and government agency securities — — Agency mortgage and asset backed securities — — Municipal bonds — — Other — — Long-term investments: International equity trust — — Corporate bonds — — US Treasury and government agency securities — — Agency mortgage and asset backed securities — — Mutual funds — — Other — — Interest rate options — — Natural gas swaps — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements at Reporting Date Using December 31, 2014 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) Nuclear decommissioning trust funds: Domestic equity $ $ $ — $ — International equity trust — — Corporate bonds — — US Treasury and government agency securities — — Agency mortgage and asset backed securities — — Municipal Bonds — — Other — — Long-term investments: Corporate bonds — — US Treasury and government agency securities — — Agency mortgage and asset backed securities — — International equity trust — — Mutual funds — — Other — — Interest rate options — — Natural gas swaps — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of changes in Level 3 assets and liabilities measured at fair value on a recurring basis	​ ​ ​ ​ ​ Three Months Ended June 30, 2015 ​ ​ ​ ​ ​ Interest rate options ​ ​ ​ ​ ​ (dollars in thousands) Assets (Liabilities): Balance at March 31, 2015 $ Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) ​ ​ ​ ​ ​ Balance at June 30, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, 2014 ​ ​ ​ ​ ​ Interest rate options ​ ​ ​ ​ ​ (dollars in thousands) Assets (Liabilities): Balance at March 31, 2014 $ Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) ) ​ ​ ​ ​ ​ Balance at June 30, 2014 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended June 30, 2015 ​ ​ ​ ​ ​ Interest rate options ​ ​ ​ ​ ​ (dollars in thousands) Assets (Liabilities): Balance at December 31, 2014 $ Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) ​ ​ ​ ​ ​ Balance at June 30, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended June 30, 2014 ​ ​ ​ ​ ​ Interest rate options ​ ​ ​ ​ ​ (dollars in thousands) Assets (Liabilities): Balance at December 31, 2013 $ Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) ) ​ ​ ​ ​ ​ Balance at June 30, 2014 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
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 June 30, 2015 and December 31, 2014 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2015 2014 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Carrying Value Fair Value Carrying Value Fair Value ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Long-term debt $ $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Derivative Instruments (Tables)

Derivative Instruments (Tables)	6 Months Ended
	Jun. 30, 2015
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 June 30, 2015 that is expected to settle or mature each year: ​ ​ ​ ​ ​ Year Natural Gas Swaps (MMBTUs) (in millions) ​ ​ ​ ​ ​ 2015 2016 2017 ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​
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 June 30, 2015. ​ ​ ​ ​ ​ Year LIBOR Swaption Notional Dollar Amount (in thousands) ​ ​ ​ ​ ​ 2015 $ 2016 2017 ​ ​ ​ ​ ​ Total $ ​ ​ ​ ​ ​
Schedule of fair value of derivative instruments and their effect on consolidated balance sheets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance Sheet Location Fair Value ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2015 2014 (dollars in thousands) Not designated as hedges: Assets: Interest rate options Other deferred charges $ $ Liabilities: Natural gas swaps Other current liabilities $ $ Natural gas swaps Other deferred credits ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of the realized gains and (losses) on derivative instruments recognized in margin	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Statement of Revenues and Expenses Three months ended June 30, Six months ended June 30, Location 2015 2014 2015 2014 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) Not Designated as hedges: Natural Gas Swaps Fuel $ $ $ $ Natural Gas Swaps Fuel ) — ) — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ ) $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of unrealized gains and (losses) on derivative instruments deferred on the balance sheet	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance Sheet Location 2015 2014 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) Not designated as hedges: Natural gas swaps Regulatory asset $ ) $ ) Interest rate options Regulatory asset ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total not designated as hedges $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
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 of Recognized Assets (Liabilities) Gross Amounts offset on the Balance Sheet Cash Collateral Net Amounts of Assets Presented on the Balance Sheet ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) June 30, 2015 Assets: Natural gas swaps $ ) $ — $ — $ ) Interest rate options $ $ ) $ — $ December 31, 2014 Assets: Natural gas swaps $ ) $ — $ — $ ) Interest rate options $ $ ) $ — $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Investments in Debt and Equit22

Investments in Debt and Equity Securities (Tables)	6 Months Ended
	Jun. 30, 2015
Investments in Debt and Equity Securities
Summary of activities for available-for-sale securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) June 30, 2015 Cost Gains Losses Fair Value ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity $ $ $ ) $ Debt ) Other — ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Unrealized ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (dollars in thousands) December 31, 2014 Cost Gains Losses Fair Value ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity $ $ $ ) $ Debt ) Other — ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ) $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Accumulated Comprehensive Mar23

Accumulated Comprehensive Margin (Deficit) (Tables)	6 Months Ended
	Jun. 30, 2015
Accumulated Comprehensive Margin (Deficit)
Schedule of changes in accumulated other comprehensive margin (deficit)	​ ​ ​ ​ ​ Accumulated Other Comprehensive Margin (Deficit) Three Months Ended June 30, 2014 ​ ​ ​ ​ ​ (dollars in thousands) Available-for-sale Securities ​ ​ ​ ​ ​ Balance at March 31, 2014 $ ) Unrealized gain (Gain) reclassified to net margin ) ​ ​ ​ ​ ​ Balance at June 30, 2014 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, 2015 ​ ​ ​ ​ ​ (dollars in thousands) Available-for-sale Securities ​ ​ ​ ​ ​ Balance at March 31, 2015 $ Unrealized loss ) (Gain) reclassified to net margin ) ​ ​ ​ ​ ​ Balance at June 30, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended June 30, 2014 ​ ​ ​ ​ ​ (dollars in thousands) Available-for-sale Securities ​ ​ ​ ​ ​ Balance at December 31, 2013 $ ) Unrealized gain (Gain) reclassified to net margin ) ​ ​ ​ ​ ​ Balance at June 30, 2014 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended June 30, 2015 ​ ​ ​ ​ ​ (dollars in thousands) Available-for-sale Securities ​ ​ ​ ​ ​ Balance at December 31, 2014 $ Unrealized loss ) (Gain) reclassified to net margin ) ​ ​ ​ ​ ​ Balance at June 30, 2015 $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Regulatory Assets and Liabili24

Regulatory Assets and Liabilities (Tables)	6 Months Ended
	Jun. 30, 2015
Regulatory Assets and Liabilities
Schedule of regulatory assets and liabilities	​ ​ ​ ​ ​ ​ ​ ​ 2015 2014 (dollars in thousands) ​ ​ ​ ​ ​ ​ ​ ​ Regulatory Assets: Premium and loss on reacquired debt (a) $ $ Amortization on capital leases (b) Outage costs (c) Interest rate swap termination fees (d) Depreciation expense (e) Deferred charges related to Vogtle Units No. 3 and No. 4 training costs (f) Interest rate options cost (g) Deferral of effects on net margin—Smith Energy Facility (h) Other regulatory assets (m) ​ ​ ​ ​ ​ ​ ​ ​ Total Regulatory Assets $ $ Regulatory Liabilities: Accumulated retirement costs for other obligations (i) $ $ Deferral of effects on net margin—Hawk Road Energy Facility (h) Major maintenance reserve (j) Amortization on capital leases (b) Deferred debt service adder (k) Asset retirement obligations (l) Other regulatory liabilities (m) ​ ​ ​ ​ ​ ​ ​ ​ Total Regulatory Liabilities $ $ ​ ​ ​ ​ ​ ​ ​ ​ Net Regulatory Assets $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (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. (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 a 24-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) 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. (f) 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. (g) Deferral of net loss associated with the change in fair value and expired cost of interest rate options purchased 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. (h) 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. (i) Represents difference in timing of recognition of retirement costs associated with long-lived assets in which there are no legal obligations to retire for financial statement purposes and for ratemaking purposes. (j) Represents collections for future major maintenance costs; revenues are recognized as major maintenance costs are incurred. (k) Represents collections to fund certain debt payments to be made through the end of 2025 which will be in excess of amounts collected through depreciation expense; the deferred credits will be amortized over the remaining useful life of the plants. (l) Represents difference in timing of recognition of the costs of decommissioning for financial statement purposes and for ratemaking purposes. (m) 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.

General (Details)

General (Details)	6 Months Ended
	Jun. 30, 2015item
General
Number of electric distribution cooperative members	38

Fair Value (Details)

Fair Value (Details) - USD ($)	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Fair value measurement
Long-term investments	$ 84,833,000	$ 85,728,000
Interest rate options
Fair value measurement
Derivative assets	4,715,000	4,371,000
Natural gas swaps
Fair value measurement
Derivative liabilities	15,942,000	18,914,000
International equity trust
Fair value measurement
Unfunded commitments	$ 0
Redemption notice period	3 days
Recurring basis | Total Fair Value | Interest rate options
Fair value measurement
Derivative assets	$ 4,715,000	4,371,000
Recurring basis | Total Fair Value | Natural gas swaps
Fair value measurement
Derivative liabilities	15,942,000	18,914,000
Recurring basis | Total Fair Value | Domestic equity
Fair value measurement
Nuclear decommissioning trust funds	155,440,000	159,536,000
Recurring basis | Total Fair Value | International equity trust
Fair value measurement
Nuclear decommissioning trust funds	74,017,000	72,474,000
Long-term investments	12,566,000	11,162,000
Recurring basis | Total Fair Value | Corporate bonds
Fair value measurement
Nuclear decommissioning trust funds	38,834,000	34,446,000
Long-term investments	6,179,000	5,445,000
Recurring basis | Total Fair Value | US Treasury and government agency securities
Fair value measurement
Nuclear decommissioning trust funds	75,625,000	68,854,000
Long-term investments	16,781,000	16,619,000
Recurring basis | Total Fair Value | Agency mortgage and asset backed securities
Fair value measurement
Nuclear decommissioning trust funds	16,108,000	16,148,000
Long-term investments	926,000	643,000
Recurring basis | Total Fair Value | Municipal Bonds
Fair value measurement
Nuclear decommissioning trust funds	916,000	743,000
Recurring basis | Total Fair Value | Mutual funds
Fair value measurement
Long-term investments	48,172,000	51,741,000
Recurring basis | Total Fair Value | Other
Fair value measurement
Nuclear decommissioning trust funds	12,296,000	13,803,000
Long-term investments	209,000	118,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity
Fair value measurement
Nuclear decommissioning trust funds	155,440,000	159,536,000
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	75,625,000	68,854,000
Long-term investments	16,781,000	16,619,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds
Fair value measurement
Long-term investments	48,172,000	51,741,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Fair value measurement
Nuclear decommissioning trust funds	12,296,000	13,803,000
Long-term investments	209,000	118,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Natural gas swaps
Fair value measurement
Derivative liabilities	15,942,000	18,914,000
Recurring basis | Significant Other Observable Inputs (Level 2) | International equity trust
Fair value measurement
Nuclear decommissioning trust funds	74,017,000	72,474,000
Long-term investments	12,566,000	11,162,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Corporate bonds
Fair value measurement
Nuclear decommissioning trust funds	38,834,000	34,446,000
Long-term investments	6,179,000	5,445,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Agency mortgage and asset backed securities
Fair value measurement
Nuclear decommissioning trust funds	16,108,000	16,148,000
Long-term investments	926,000	643,000
Recurring basis | Significant Other Observable Inputs (Level 2) | Municipal Bonds
Fair value measurement
Nuclear decommissioning trust funds	916,000	743,000
Recurring basis | Significant Unobservable Inputs (Level 3) | Interest rate options
Fair value measurement
Derivative assets	$ 4,715,000	$ 4,371,000

Fair Value (Details 2)

Fair Value (Details 2) - Interest rate options - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Assets (Liabilities):
Balance at the beginning of the period	$ 2,702	$ 31,463	$ 4,371	$ 63,471
Total gains or losses (realized/unrealized):
Included in earnings (or changes in net assets)	2,013	(12,928)	344	(44,936)
Balance at the end of the period	$ 4,715	$ 18,535	$ 4,715	$ 18,535

Fair Value (Details 3)

Fair Value (Details 3) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Carrying Value
Grouping Financial Statement Captions
Long-term debt	$ 7,476,491	$ 7,256,995
Total Fair Value
Grouping Financial Statement Captions
Long-term debt	$ 8,281,385	$ 8,460,685

Derivative Instruments (Details

Derivative Instruments (Details) - Natural gas swaps item in Millions	Jun. 30, 2015USD ($)item	Dec. 31, 2014USD ($)
Gas hedges
Derivative liabilities | $	$ 15,942,000	$ 18,914,000
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 | $	$ 16,158,000
Derivative volume activity that is expected to settle or mature each year (in MMBTUs)	29.9
2,015
Gas hedges
Derivative volume activity that is expected to settle or mature each year (in MMBTUs)	12.9
2,016
Gas hedges
Derivative volume activity that is expected to settle or mature each year (in MMBTUs)	13.8
2,017
Gas hedges
Derivative volume activity that is expected to settle or mature each year (in MMBTUs)	3.2

Derivative Instruments (Detai30

Derivative Instruments (Details 2) - Interest rate options	3 Months Ended	6 Months Ended
	Dec. 31, 2011USD ($)item	Jun. 30, 2015USD ($)	Dec. 31, 2014USD ($)
Derivative instruments and hedging activities
Purchased amount of derivative instrument	$ 100,000,000
Notional Dollar Amount	$ 2,200,000,000	$ 629,520,000
Number of nuclear units expected to be financed | item	2
Derivative notional amount expired		1,549,683,000
Derivative remaining notional amount		629,520,000
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)		3.98%
Notional amount of derivatives, expired without value		$ 231,806,000
Fair value of assets		4,715,000	$ 4,371,000
Funds posted as collateral by the counterparties		0	$ 0
2,015
Derivative instruments and hedging activities
Notional Dollar Amount		238,818,000
2,016
Derivative instruments and hedging activities
Notional Dollar Amount		310,533,000
2,017
Derivative instruments and hedging activities
Notional Dollar Amount		$ 80,169,000
LIBOR
Derivative instruments and hedging activities
Variable rate basis		LIBOR
Minimum
Derivative instruments and hedging activities
Collateral thresholds range		$ 0
Maximum
Derivative instruments and hedging activities
Collateral thresholds range		$ 10,000,000
Average | LIBOR
Derivative instruments and hedging activities
Basis spread (as a percent)		1.27%
Department of Energy-guaranteed loan
Derivative instruments and hedging activities
Hedged amount of expected debt		$ 2,200,000,000

Derivative Instruments (Detai31

Derivative Instruments (Details 3) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Interest rate options
Assets:
Fair value of assets	$ 4,715,000	$ 4,371,000
Natural gas swaps
Liabilities:
Fair Value of liabilities	15,942,000	18,914,000
Not designated as hedges | Interest rate options | Other Deferred Charges
Assets:
Fair value of assets	4,715,000	4,371,000
Not designated as hedges | Natural gas swaps | Other Current Liabilities
Liabilities:
Fair Value of liabilities	10,198,000	13,418,000
Not designated as hedges | Natural gas swaps | Other Deferred Credits
Liabilities:
Fair Value of liabilities	$ 5,744,000	$ 5,496,000

Derivative Instruments (Detai32

Derivative Instruments (Details 4) - Not designated as hedges - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Effect of Derivative Instruments on the Condensed Statement of Revenues and Expenses or Balance Sheet
Unrealized gains and (losses) on derivatives	$ (52,265)		$ (52,265)		$ (68,146)
Natural gas swaps | Regulatory Asset
Effect of Derivative Instruments on the Condensed Statement of Revenues and Expenses or Balance Sheet
Unrealized losses on derivatives	(15,942)		(15,942)		(18,914)
Natural gas swaps | Fuel
Effect of Derivative Instruments on the Condensed Statement of Revenues and Expenses or Balance Sheet
Gains	181	$ 956	181	$ 1,236
Losses	(3,248)		(8,775)
Total gains (losses) on derivatives	(3,067)	$ 956	(8,594)	$ 1,236
Interest rate options | Regulatory Asset
Effect of Derivative Instruments on the Condensed Statement of Revenues and Expenses or Balance Sheet
Unrealized losses on derivatives	$ (36,323)		$ (36,323)		$ (49,232)

Derivative Instruments (Detai33

Derivative Instruments (Details 5) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Natural gas swaps
Liabilities:
Gross Amounts of Recognized Assets (Liabilities)	$ (15,942)	$ (18,914)
Net Amounts of (Liabilities) Presented on the Balance Sheet	(15,942)	(18,914)
Interest rate options
Assets:
Gross Amounts of Recognized Assets (Liabilities)	41,038	53,603
Gross Amounts offset on the Balance Sheets	(36,323)	(49,232)
Net Amounts of Assets Presented on the Balance Sheet	$ 4,715	$ 4,371

Investments in Debt and Equit34

Investments in Debt and Equity Securities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
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)	61.00%
Available-for-sale securities
Cost	$ 416,431	$ 383,001
Gains	47,423	79,517
Losses	(5,785)	(10,786)
Fair Value	458,069	451,732
Equity
Available-for-sale securities
Cost	225,613	200,892
Gains	45,528	69,536
Losses	(3,455)	(2,163)
Fair Value	267,686	268,265
Debt.
Available-for-sale securities
Cost	178,312	168,182
Gains	1,895	9,981
Losses	(2,328)	(8,619)
Fair Value	177,879	169,544
Other
Available-for-sale securities
Cost	12,506	13,927
Losses	(2)	(4)
Fair Value	$ 12,504	$ 13,923

Accumulated Comprehensive Mar35

Accumulated Comprehensive Margin (Deficit) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Comprehensive Margin (Deficit)
Effective income tax rate (as a percent)			0.00%
Accumulated Comprehensive Margin (Deficit)
Balance at the beginning of the period	$ 421	$ (153)	$ 468	$ (549)
Unrealized gain (loss)	(161)	492	(54)	881
(Gain) reclassified to net margin	(153)	(61)	(307)	(54)
Balance at the end of the period	$ 107	$ 278	$ 107	$ 278

Contingencies and Regulatory 36

Contingencies and Regulatory Matters (Details)	Aug. 20, 2014item	Jul. 28, 2014item	Mar. 13, 2014item	Apr. 30, 2008itemMW	Jun. 30, 2015USD ($)item	May. 22, 2014USD ($)	Dec. 31, 2008USD ($)
Nuclear Construction
Number of Electric Distribution Cooperative Members					38
Vogtle Units Number 3 And Number 4
Nuclear Construction
Number of Westinghouse AP1000 nuclear generating units				2
Nominally rated generating capacity for each unit | MW				1,100
Aggregate Damages Under Initial Complaint And Amended Counterclaim | Vogtle Units Number 3 And Number 4
Nuclear Construction
Contractor's estimated adjustment attributable to the entity | $					$ 470,000,000
Costs Associated With Design Changes Delays In Project Schedule And Issuance Of Combined Construction Permits And Operating Licenses | Vogtle Units Number 3 And Number 4
Nuclear Construction
Contractor's estimated adjustment attributable to the entity | $					390,000,000		$ 280,000,000
Amended counterclaim associated with design changes, delays in Project Schedule and issuance of permits and operating licenses | Vogtle Units Number 3 And Number 4
Nuclear Construction
Contractor's estimated adjustment attributable to the entity | $					$ 78,000,000	$ 75,000,000
Patronage Capital Litigation
Nuclear Construction
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
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%
Number of current consumer members	2
Number of plaintiffs	3
Patronage Capital Litigation | Maximum
Nuclear Construction
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

Restricted Cash and Investmen37

Restricted Cash and Investments (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Restricted Cash and Investments.
Guaranteed interest rate on deposit with Rural Utilities Service (as a percent)	5.00%	5.00%
Restricted Cash and Investments	$ 329,253,000	$ 365,585,000
Restricted Cash And Investments, Noncurrent	$ 76,535,000	$ 118,390,000

Regulatory Assets and Liabili38

Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Regulatory assets and liabilities
Total Regulatory Assets	$ 513,026	$ 484,049
Total Regulatory Liabilities	192,970	194,073
Net Regulatory Assets	320,056	289,976
Accumulated retirement costs for other obligations
Regulatory assets and liabilities
Total Regulatory Liabilities	14,332	18,559
Deferral of effects on net margin- Hawk Road Energy Facility | Hawk Road
Regulatory assets and liabilities
Total Regulatory Liabilities	28,622	29,867
Major maintenance reserve
Regulatory assets and liabilities
Total Regulatory Liabilities	19,133	23,427
Amortization on capital leases
Regulatory assets and liabilities
Total Regulatory Liabilities	26,198	21,693
Deferred debt service adder
Regulatory assets and liabilities
Total Regulatory Liabilities	71,527	66,754
Asset retirement obligations
Regulatory assets and liabilities
Total Regulatory Liabilities	28,277	28,870
Other regulatory liabilities
Regulatory assets and liabilities
Total Regulatory Liabilities	$ 4,881	4,903
Other regulatory liabilities | Maximum
Regulatory assets and liabilities
Amortization period	18 years
Premium and loss on reacquired debt
Regulatory assets and liabilities
Total Regulatory Assets	$ 66,823	71,731
Premium and loss on reacquired debt | Maximum
Regulatory assets and liabilities
Amortization period	30 years
Amortization on capital leases
Regulatory assets and liabilities
Total Regulatory Assets	$ 29,041	27,829
Outage costs
Regulatory assets and liabilities
Total Regulatory Assets	41,616	45,795
Interest rate swap termination fees
Regulatory assets and liabilities
Total Regulatory Assets	7,350	9,345
Depreciation expense
Regulatory assets and liabilities
Total Regulatory Assets	$ 46,226	46,938
Depreciation expense | Plant Vogtle
Regulatory assets and liabilities
Operating license expected extension period for Plant Vogtle	20 years
Operating license, expected extension period, for Plant Vogtle	40 years
Deferred charges related to Vogtle Units No. 3 and No. 4 training costs | Vogtle Units Number 3 And Number 4
Regulatory assets and liabilities
Total Regulatory Assets	$ 35,083	32,501
Interest rate options cost
Regulatory assets and liabilities
Total Regulatory Assets	98,577	98,671
Deferral of effects on net margin - Smith Energy Facility | Smith
Regulatory assets and liabilities
Total Regulatory Assets	169,188	128,666
Other regulatory assets
Regulatory assets and liabilities
Total Regulatory Assets	$ 19,122	$ 22,573
Other regulatory assets | Maximum
Regulatory assets and liabilities
Amortization period	35 years
Coal-fired outage costs
Regulatory assets and liabilities
Amortization period	24 months
Nuclear refueling outage costs | Minimum
Regulatory assets and liabilities
Amortization period	18 months
Nuclear refueling outage costs | Maximum
Regulatory assets and liabilities
Amortization period	24 months

Debt (Details)

Debt (Details)	Mar. 23, 2015USD ($)item	Feb. 20, 2014USD ($)	Jul. 31, 2015USD ($)	Jun. 30, 2015USD ($)item	Jun. 12, 2015USD ($)
Facility
Debt
Number of future advance promissory notes | item				2
Aggregate borrowings including capitalized interest				$ 1,036,135,000
Principal amount					$ 145,000,000
Facility | Maximum
Debt
Aggregate borrowings expressed as a percentage of Eligible Project Costs		70.00%
Aggregate borrowings		$ 3,057,069,461
Maximum interest accrued under Facility		$ 335,471,604
Rural Utilities Service Guaranteed Loans
Debt
Principal amount			$ 18,018,000	$ 126,892,000
Committed credit arrangements
Debt
Term of credit facility	5 years
Aggregate borrowings	$ 1,210,000,000
Number of lenders | item	13

Nuclear Fuel Disposal Cost Li40

Nuclear Fuel Disposal Cost Litigation (Details) - Nuclear Fuel Disposal Cost Settlement, January 1, 2005 through December 31, 2010 - Plant Hatch and Plant Vogtle - USD ($)	1 Months Ended	3 Months Ended
	Apr. 30, 2015	Mar. 31, 2015	Dec. 14, 2014
Nuclear Fuel Disposal Cost Litigation
Settlement amount, all parties			$ 36,474,000
Settlement amount, entity share	$ 10,949,000
Reduction of total operating expenses		$ 7,320,000
Reduction to plant in service		$ 3,629,000

Asset Retirement Obligations (D

Asset Retirement Obligations (Details)	3 Months Ended
	Jun. 30, 2015USD ($)
Asset Retirement Obligation Disclosure
Change in Cash Flow Estimates	$ 20,711,000