Consolidated Statement of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating activities [Abstract]
Net income	$ 38,955	$ 39,765
Adjustments to reconcile net income to cash provided by operations [Abstract]
Depreciation and amortization	39,298	37,737
Regulatory amortization of gas reserves	8,680	4,970
Deferred tax liabilities, net	989	28,401
Non-cash expenses related to qualified defined benefit pension plans	2,540	2,773
Contributions to qualified defined benefit pension plans	(6,000)	(4,200)
Deferred environmental recoveries, net of expenditures	92,104	(2,989)
Other	1,010	(1,567)
Changes in assets and liabilities [Abstract]
Receivables	89,951	63,102
Inventories	(139)	5,190
Taxes accrued	8,447	(1,535)
Accounts payable	(24,472)	(22,155)
Interest accrued	(50)	451
Deferred gas costs	(18,812)	(648)
Other, net	744	10,847
Cash provided by operating activities	233,245	160,142
Investing activities [Abstract]
Capital expenditures	(52,489)	(55,055)
Utility gas reserves	(18,632)	(34,397)
Proceeds from Sale of Productive Assets	0	6,580
Increase (Decrease) in Restricted Cash	1,000	0
Other	(1,043)	1,743
Cash used in investing activities	(71,164)	(81,129)
Financing activities [Abstract]
Common stock issued, net	3,733	2,355
Repayments of Long-term Debt	(20,000)	0
Change in short-term debt	(114,000)	(54,250)
Cash dividend payments on common stock	(24,938)	(24,509)
Other	893	682
Cash used in financing activities	(154,312)	(75,722)
Increase (decrease) in cash and cash equivalents	7,769	3,291
Cash and cash equivalents, beginning of period	9,471	8,923
Cash and cash equivalents, end of period	17,240	12,214
Supplemental disclosure of cash flow information [Abstract]
Interest paid	23,270	21,746
Income taxes paid	$ 14,945	$ 0