Consolidated Statement of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Operating activities [Abstract]
Net income	$ 30,222	$ 31,532
Adjustments to reconcile net income to cash provided by operations [Abstract]
Depreciation and amortization	59,236	56,474
Regulatory amortization of gas reserves	13,795	8,132
Deferred tax liabilities, net	10,721	22,003
Non-cash expenses related to qualified defined benefit pension plans	3,795	4,256
Contributions to qualified defined benefit pension plans	(10,500)	(8,900)
Deferred environmental recoveries, net of (expenditures)	89,537	(10,805)
Other	(1,692)	(2,116)
Changes in assets and liabilities [Abstract]
Receivables	100,931	70,154
Inventories	(25,931)	(7,817)
Taxes accrued	(3,085)	3,357
Accounts payable	(28,762)	(19,860)
Interest accrued	3,324	5,190
Deferred gas costs	(22,173)	(4,159)
Other, net	(4,554)	9,961
Cash provided by operating activities	214,864	157,402
Investing activities [Abstract]
Capital expenditures	(86,552)	(86,287)
Utility gas reserves	(21,734)	(41,777)
Proceeds from Sale of Productive Assets	0	6,580
Increase (Decrease) in Restricted Cash	1,000	0
Other	82	2,116
Cash used in investing activities	(107,204)	(119,368)
Financing activities [Abstract]
Common stock issued, net	5,460	3,754
Proceeds from Issuance of Long-term Debt	0	50,000
Repayments of Long-term Debt	(80,000)	0
Change in short-term debt	1,800	(48,950)
Cash dividend payments on common stock	(37,442)	(36,783)
Other	1,326	1,127
Cash used in financing activities	(108,856)	(30,852)
Increase (decrease) in cash and cash equivalents	(1,196)	7,182
Cash and cash equivalents, beginning of period	9,471	8,923
Cash and cash equivalents, end of period	8,275	16,105
Supplemental disclosure of cash flow information [Abstract]
Interest paid	30,701	28,353
Income taxes paid	$ 14,945	$ 570