Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Current assets:
Cash and cash equivalents	$ 4,031	$ 5,833	$ 3,480
Restricted cash	0	0	924
Accounts receivable	90,817	77,449	94,521
Accrued unbilled revenue	44,444	61,925	42,342
Allowance for uncollectible accounts	(3,694)	(2,895)	(3,821)
Regulatory assets	90,490	94,673	48,195
Derivative instruments	1,824	2,853	4,861
Inventories	61,436	74,363	53,266
Gas Reserves	6,732	4,463	0
Income taxes receivable	1,735	7,045	23,645
Other current assets	13,075	22,980	13,292
Total current assets	310,890	348,689	280,705
Non-current assets:
Property, plant and equipment	2,680,537	2,661,102	2,593,553
Less: Accumulated depreciation	779,683	767,226	733,639
Total property, plant and equipment - net	1,900,854	1,893,876	1,859,914
Gas Reserves	61,106	47,451	0
Regulatory Assets	368,521	371,392	345,452
Derivative instruments	52	0	1,560
Other investments	67,648	68,263	69,501
Restricted cash	4,000	4,000	0
Other non-current assets	14,191	12,903	14,421
Total non-current assets	2,416,372	2,397,885	2,290,848
Total assets	2,727,262	2,746,574	2,571,553
Capitalization:
Common stock - no par value; authorized 100,000 shares; issued and outstanding 26,673, 26,564 and 26,668 at March 31, 2011 and 2010, and December 31, 2010, respectively	351,005	348,383	343,787
Retained earnings	402,599	373,905	385,899
Accumulated other comprehensive income (loss)	(7,633)	(7,800)	(6,458)
Total common stock equity	745,971	714,488	723,228
Long-term debt	641,700	641,700	551,700
Total capitalization	1,387,671	1,356,188	1,274,928
Current liabilities:
Short-term debt	113,700	141,600	186,435
Current maturities of long-term debt	0	40,000	50,000
Accounts payable	60,165	86,300	71,839
Taxes accrued	10,509	10,747	10,063
Interest accrued	10,648	5,857	11,470
Regulatory liabilities	50,341	31,046	29,016
Derivative instruments	53,697	57,317	25,655
Other current liabilities	41,503	41,597	38,433
Total current liabilities	340,563	414,464	422,911
Deferred credits and other non-current liabilities:
Deferred tax liabilities	438,486	413,209	396,357
Regulatory Liabilities	288,131	278,382	263,876
Pension and other postretirement benefit liabilities	189,003	201,530	132,053
Derivative instruments	3,947	6,536	13,914
Other non-current liabilities	79,461	76,265	67,514
Total deferred credits and other non-current liabilities	999,028	975,922	873,714
Total capitalization and liabilities	$ 2,727,262	$ 2,746,574	$ 2,571,553