Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Electric plant:
In service	$ 7,678,439	$ 7,506,707
Less: Accumulated provision for depreciation	(3,541,332)	(3,472,087)
Total in service	4,137,107	4,034,620
Nuclear fuel, at amortized cost	314,660	321,196
Construction work in progress	2,329,218	2,240,920
Total electric plant	6,780,985	6,596,736
Investments and funds:
Nuclear decommissioning trust fund	311,590	300,785
Deposit on Rocky Mountain transactions	14,878	14,392
Investment in associated companies	63,109	60,770
Long-term investments	77,634	77,022
Restricted cash	36,074	8,953
Other	472	1,084
Total investments and funds	503,757	463,006
Current assets:
Cash and cash equivalents	220,650	298,565
Restricted short-term investments	206,211	64,671
Receivables	162,379	134,896
Inventories, at average cost	267,851	263,949
Prepayments and other current assets	17,945	16,073
Total current assets	875,036	778,154
Deferred charges:
Deferred debt expense, being amortized	64,738	63,210
Regulatory assets	356,595	352,902
Other	48,410	60,558
Total deferred charges	469,743	476,670
Total assets	8,629,521	8,314,566
Capitalization:
Patronage capital and membership fees	719,535	673,009
Accumulated other comprehensive (deficit) margin	(399)	903
Total patronage capital and membership fees and accumulated other comprehensive margin	719,136	673,912
Long-term debt	5,770,689	5,784,130
Obligation under capital leases	128,962	135,943
Obligation under Rocky Mountain transactions	14,878	14,392
Total capitalization	6,633,665	6,608,377
Current liabilities:
Long-term debt and capital leases due within one year	460,615	168,393
Short-term borrowings	538,261	569,480
Accounts payable	78,531	145,451
Accrued interest	89,671	58,649
Accrued and withheld taxes	17,689	4,881
Member power bill prepayments, current	124,090	65,079
Other current liabilities	16,387	19,539
Total current liabilities	1,325,244	1,031,472
Deferred credits and other liabilities:
Gain on sale of plant, being amortized	22,898	23,638
Asset retirement obligations	389,301	381,362
Member power bill prepayments, non-current	32,702	40,853
Power sale agreement, being amortized	33,231	40,355
Regulatory liabilities	131,819	129,985
Other	60,661	58,524
Total deferred credits and other liabilities	670,612	674,717
Total equity and liabilities	$ 8,629,521	$ 8,314,566