CONDENSED CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (UNAUDITED) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 50,704	$ 26,187
Accounts receivable	103,585	72,192
Inventory	36,282	37,357
Deferred income taxes	18,925	23,014
Regulatory assets — revenue accruals, including accrued interest	6,620	7,489
Prepaid and other current assets	18,053	31,987
Total current assets	234,169	198,226
Property, plant and equipment (net of accumulated depreciation and amortization of $1,319,710 and $1,269,810, respectively)	4,687,581	4,134,579
Other assets
Goodwill	950,163	950,163
Intangible assets (net of accumulated amortization of $20,801 and $18,397, respectively)	49,431	48,492
Other regulatory assets	186,926	180,378
Deferred financing fees (net of accumulated amortization of $14,390 and $17,838, respectively)	26,279	19,293
Other	37,851	33,678
Total other assets	1,250,650	1,232,004
TOTAL ASSETS	6,172,400	5,564,809
Current liabilities
Accounts payable	105,285	123,022
Accrued payroll	17,738	20,740
Accrued interest	30,170	44,708
Accrued taxes	17,650	28,117
Regulatory liabilities — revenue deferrals, including accrued interest	38,296	53,763
Refundable deposits from generators for transmission network upgrades	29,656	40,745
Debt maturing within one year	210,000	651,929
Other	16,759	40,287
Total current liabilities	465,554	1,003,311
Accrued pension and postretirement liabilities	58,395	53,243
Deferred income taxes	555,038	460,072
Regulatory liabilities — revenue deferrals, including accrued interest	74,223	28,613
Regulatory liabilities — accrued asset removal costs	70,226	75,477
Refundable deposits from generators for transmission network upgrades	15,392	7,623
Other	20,139	26,317
Long-term debt	3,364,900	2,495,298
Commitments and contingent liabilities (Note 11)
STOCKHOLDERS’ EQUITY
Common stock, without par value, 100,000,000 shares authorized, 52,471,354 and 52,248,514 shares issued and outstanding at September 30, 2013 and December 31, 2012, respectively	1,003,709	989,334
Retained earnings	538,317	443,569
Accumulated other comprehensive income (loss)	6,507	(18,048)
Total stockholders’ equity	1,548,533	1,414,855
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 6,172,400	$ 5,564,809