Consolidated Statements Of Operations (USD $) In Thousands, except Share data	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Consolidated Statements Of Operations
Operating revenues	$ 307,633	$ 280,342	$ 726,350	$ 695,907	$ 907,694	$ 888,920
Energy expenses:
Fuel	73,034	60,294	177,111	160,139	216,801	205,849
Purchased and interchanged power	25,845	28,229	60,616	76,628	75,904	99,660
Cost of services, energy services, total	98,879	88,523	237,727	236,767	292,705	305,509
Operating revenues net of energy expenses	208,754	191,819	488,623	459,140	614,989	583,411
Other operating expenses:
Other operations	56,832	59,924	168,148	161,566	230,803	222,466
Maintenance	12,764	10,987	41,760	41,222	57,361	58,872
Depreciation and amortization	20,315	20,685	60,775	60,136	81,650	79,501
Taxes other than income taxes	16,628	16,125	43,131	41,038	56,582	52,413
Utilities operating expense, total	106,539	107,721	313,814	303,962	426,396	413,252
Operating income	102,215	84,098	174,809	155,178	188,593	170,159
Other income (deductions):
Allowance for equity funds used during construction	1,379	2,398	6,441	7,645	9,612	9,575
Investment and interest income, net	618	1,351	4,593	3,289	6,619	7,333
Miscellaneous non-operating income	113	248	384	401	1,351	423
Miscellaneous non-operating deductions	(648)	(389)	(2,061)	(1,277)	(3,990)	(1,866)
Nonoperating income (expense), total	1,462	3,608	9,357	10,058	13,592	15,465
Interest charges (credits):
Interest on long-term debt and revolving credit facility	13,571	12,936	40,595	37,378	54,043	49,576
Other interest	243	48	777	113	918	190
Capitalized interest	(1,318)	(796)	(3,864)	(1,282)	(5,069)	(1,504)
Allowance for borrowed funds used during construction	(808)	(1,550)	(3,837)	(4,651)	(5,857)	(5,910)
Interest expense, total	11,688	10,638	33,671	31,558	44,035	42,352
Income before income taxes and extraordinary item	91,989	77,068	150,495	133,678	158,150	143,272
Income tax expense	33,668	27,172	52,409	50,826	52,599	52,459
Income before extraordinary item	58,321	49,896	98,086	82,852	105,551	90,813
Extraordinary gain related to Texas regulatory assets, net of tax	0	10,286	0	10,286	0	10,286
Net income	$ 58,321	$ 60,182	$ 98,086	$ 93,138	$ 105,551	$ 101,099
Basic earnings per share:
Income before extraordinary item	$ 1.41	$ 1.16	$ 2.33	$ 1.90	$ 2.50	$ 2.07
Extraordinary gain related to Texas regulatory assets, net of tax	$ 0.00	$ 0.24	$ 0.00	$ 0.24	$ 0.00	$ 0.24
Basic net income per common share	$ 1.41	$ 1.40	$ 2.33	$ 2.14	$ 2.50	$ 2.31
Diluted earnings per share:
Income before extraordinary item	$ 1.40	$ 1.15	$ 2.32	$ 1.89	$ 2.49	$ 2.07
Extraordinary gain related to Texas regulatory assets, net of tax	$ 0.00	$ 0.24	$ 0.00	$ 0.24	$ 0.00	$ 0.24
Diluted net income per common share	$ 1.40	$ 1.39	$ 2.32	$ 2.13	$ 2.49	$ 2.31
Dividends declared per share of common stock	$ 0.22	$ 0.00	$ 0.44	$ 0.00	$ 0.44	$ 0.00
Weighted average number of shares outstanding	41,307,632	42,921,044	41,819,428	43,370,487	41,969,628	43,523,270
Weighted average number of shares and dilutive potential shares outstanding	41,564,973	43,103,698	42,051,307	43,505,434	42,207,012	43,672,324