Consolidated Statement of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Operating activities [Abstract]
Net income	$ 31,458	$ 34,654
Adjustments to reconcile net income to cash provided by operations [Abstract]
Depreciation and amortization	54,330	52,304
Non-cash expenses related to qualified defined benefit pension plans	4,334	5,491
Contributions to qualified defined benefit pension plans	(23,500)	(19,245)
Deferred environmental expenditures - net of recoveries	(6,500)	(7,018)
Other	2,612	(615)
Changes in assets and liabilities [Abstract]
Receivables	106,620	92,840
Inventories	1,175	(3,196)
Taxes accrued	4,780	36,585
Accounts payable	(24,888)	(33,369)
Interest accrued	4,736	6,139
Deferred gas costs	(15,406)	370
Deferred tax liabilities	24,503	22,908
Other - net	13,808	3,440
Cash provided by operating activities	178,062	191,288
Investing activities [Abstract]
Capital expenditures	(100,880)	(70,036)
Utility gas reserves	(41,775)	(30,917)
Restricted cash	0	924
Other	107	(192)
Cash used in investing activities	(142,548)	(100,221)
Financing activities [Abstract]
Common stock issued - net, including common stock expense	4,858	1,320
Long-term debt issued	0	50,000
Long-term debt redeemed	(40,000)	(10,000)
Change in short-term debt	34,200	(76,235)
Cash dividend payments on common stock	(35,779)	(34,807)
Other	1,092	1,060
Cash used in financing activities	(35,629)	(68,662)
Increase (decrease) in cash and cash equivalents	(115)	22,405
Cash and cash equivalents - beginning of period	5,833	3,457
Cash and cash equivalents - end of period	5,718	25,862
Supplemental disclosure of cash flow information [Abstract]
Interest paid	27,427	24,817
Income taxes paid	$ 2,333	$ 1,522