Consolidated Statements Of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011
Operating revenues	$ 168,578	$ 176,112	$ 910,479	$ 849,195
Energy expenses:
Fuel	39,434	42,759	220,182	193,495
Purchased and interchanged power	12,559	18,474	69,234	81,543
Cost of services, energy services	51,993	61,233	289,416	275,038
Operating revenues net of energy expenses	116,585	114,879	621,063	574,157
Other operating expenses:
Other operations	54,417	54,107	229,880	228,230
Maintenance	15,968	12,236	65,824	54,559
Depreciation and amortization	20,518	20,936	80,913	82,663
Taxes other than income taxes	13,640	13,127	56,074	55,873
Utilities operating expense	104,543	100,406	432,691	421,325
Operating income	12,042	14,473	188,372	152,832
Other income (deductions):
Allowance for equity funds used during construction	1,956	3,051	7,066	11,327
Investment and interest income, net	1,776	2,385	5,055	6,602
Miscellaneous non-operating income	70	270	685	1,636
Miscellaneous non-operating deductions	(482)	(715)	(2,954)	(3,562)
Nonoperating income (expense)	3,320	4,991	9,852	16,003
Interest charges (credits):
Interest on long-term debt and revolving credit facility	13,563	13,498	54,180	52,123
Other interest	200	297	892	511
Capitalized interest	(1,369)	(1,256)	(5,290)	(3,515)
Allowance for borrowed funds used during construction	(1,153)	(1,849)	(4,152)	(6,953)
Interest expense	11,241	10,690	45,630	42,166
Income before income taxes and extraordinary item	4,121	8,774	152,594	126,669
Income tax expense	777	1,999	52,486	41,026
Income before extraordinary item	3,344	6,775	100,108	85,643
Extraordinary gain related to Texas regulatory assets, net of tax	0	0	0	10,286
Net income	$ 3,344	$ 6,775	$ 100,108	$ 95,929
Basic earnings per share:
Income before extraordinary item (in dollars per share)	$ 0.08	$ 0.16	$ 2.45	$ 1.99
Extraordinary gain related to Texas regulatory assets, net of tax (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.24
Net income (in dollars per share)	$ 0.08	$ 0.16	$ 2.45	$ 2.23
Diluted earnings per share:
Income before extraordinary item (in dollars per share)	$ 0.08	$ 0.16	$ 2.43	$ 1.98
Extraordinary gain related to Texas regulatory assets, net of tax (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.24
Net income (in dollars per share)	$ 0.08	$ 0.16	$ 2.43	$ 2.22
Dividends declared per share of common stock	$ 0.22	$ 0.00	$ 0.88	$ 0.00
Weighted average number of shares outstanding	39,911,032	42,308,097	40,756,509	42,776,922
Weighted average number of shares and dilutive potential shares outstanding	39,999,509	42,523,285	40,962,007	42,964,190