Consolidated Statement of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Operating activities [Abstract]
Net income	$ 23,998	$ 30,222
Adjustments to reconcile net income to cash provided by operations [Abstract]
Depreciation and amortization	60,683	59,236
Regulatory amortization of gas reserves	13,606	13,795
Deferred tax liabilities, net	7,153	10,721
Non-cash expenses related to qualified defined benefit pension plans	4,238	3,795
Contributions to qualified defined benefit pension plans	(11,780)	(10,500)
Deferred environmental (expenditures), net of recoveries	(8,063)	89,537
Non-cash regulatory disallowance of prior environmental cost deferrals	15,000	0
non-cash interest income deferred environmental expenses	(5,322)	0
Other	669	(1,692)
Changes in assets and liabilities [Abstract]
Receivables	82,586	100,931
Inventories	(3,142)	(25,931)
Taxes accrued	2,823	(3,085)
Accounts payable	(36,230)	(28,762)
Interest accrued	3,721	3,324
Deferred gas costs	27,042	(22,173)
Other, net	(4,237)	(4,554)
Cash provided by operating activities	172,745	214,864
Investing activities [Abstract]
Capital expenditures	(86,923)	(86,552)
Utility gas reserves	(1,165)	(21,734)
Increase (Decrease) in Restricted Cash	(1,500)	1,000
Other	1,346	82
Cash used in investing activities	(88,242)	(107,204)
Financing activities [Abstract]
Common stock issued, net	1,252	5,460
Repayments of Long-term Debt	(40,000)	(80,000)
Change in short-term debt	(9,500)	1,800
Cash dividend payments on common stock	(38,122)	(37,442)
Other	(2,440)	1,326
Cash used in financing activities	(88,810)	(108,856)
Decrease in cash and cash equivalents	(4,307)	(1,196)
Cash and cash equivalents, beginning of period	9,534	9,471
Cash and cash equivalents, end of period	5,227	8,275
Supplemental disclosure of cash flow information [Abstract]
Interest paid	25,264	30,701
Income Taxes Paid, Net	$ 10,631	$ 14,945