Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Electric plant:
In service	$ 7,530,380	$ 7,506,707
Less: Accumulated provision for depreciation	(3,505,489)	(3,472,087)
Total in service	4,024,891	4,034,620
Nuclear fuel, at amortized cost	329,626	321,196
Construction work in progress	2,367,023	2,240,920
Total electric plant	6,721,540	6,596,736
Investments and funds:
Nuclear decommissioning trust fund	315,403	300,785
Deposit on Rocky Mountain transactions	14,635	14,392
Investment in associated companies	61,700	60,770
Long-term investments	79,062	77,022
Restricted cash	13,363	8,953
Other	1,083	1,084
Total investments and funds	485,246	463,006
Current assets:
Cash and cash equivalents	239,514	298,565
Restricted short-term investments	203,798	64,671
Receivables	128,528	134,896
Inventories, at average cost	253,768	263,949
Prepayments and other current assets	14,855	16,073
Total current assets	840,463	778,154
Deferred charges:
Deferred debt expense, being amortized	62,590	63,210
Regulatory assets	361,614	352,902
Other	54,156	60,558
Total deferred charges	478,360	476,670
Total assets	8,525,609	8,314,566
Capitalization:
Patronage capital and membership fees	695,033	673,009
Accumulated other comprehensive margin	691	903
Total patronage capital and membership fees and accumulated other comprehensive margin	695,724	673,912
Long-term debt	5,776,039	5,784,130
Obligation under capital leases	133,249	135,943
Obligation under Rocky Mountain transactions	14,635	14,392
Total capitalization	6,619,647	6,608,377
Current liabilities:
Long-term debt and capital leases due within one year	197,041	168,393
Short-term borrowings	708,664	569,480
Accounts payable	75,623	145,451
Accrued interest	73,100	58,649
Accrued and withheld taxes	9,515	4,881
Member power bill prepayments, current	158,132	65,079
Other current liabilities	14,271	19,539
Total current liabilities	1,236,346	1,031,472
Deferred credits and other liabilities:
Gain on sale of plant, being amortized	23,268	23,638
Asset retirement obligations	383,774	381,362
Member power bill prepayments, non-current	32,702	40,853
Power sale agreement, being amortized	36,793	40,355
Regulatory liabilities	133,401	129,985
Other	59,678	58,524
Total deferred credits and other liabilities	669,616	674,717
Total equity and liabilities	$ 8,525,609	$ 8,314,566