Consolidated Statement of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating activities: [Abstract]
Net Income	$ 30,620	$ 23,998
Adjustments to reconcile net income to cash provided by operations: [Abstract]
Depreciation and amortization	61,435	60,683
Regulatory amortization of gas reserves	11,403	13,606
Deferred Tax Liabilities, net	17,810	7,153
Qualified defined benefit pension plan expense	3,989	4,238
Contributions to qualified defined benefit pension plans	(11,250)	(11,780)
Deferred environmental (expenditures) recoveries, net of recoveries	(8,302)	(8,063)
Regulatory disallowance of prior environmental cost deferrals	3,287	15,000
Interest income on deferred environmental expenses	0	(5,322)
Amortization of environmental remediation	8,113	0
Other	4,817	669
Changes in assets and liabilities: [Abstract]
Receivables, net	83,377	82,586
Inventories	3,226	(3,142)
Taxes Accrued	7,170	2,823
Accounts payable	(17,612)	(36,230)
Interest accrued	3,798	3,721
Deferred gas costs	(10,470)	27,042
Other, net	14,988	(4,237)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations	206,399	172,745
Payments to Acquire Property, Plant, and Equipment [Abstract]
Capital expenditures	(98,111)	(86,923)
Restricted cash	0	1,500
Other	2,868	181
Net Cash Provided by (Used in) Investing Activities, Continuing Operations	(95,243)	(88,242)
Financing activities: [Abstract]
Common Stock Issued, net	4,832	1,252
Long-term debt retired	0	40,000
Change in short-term debt	(75,135)	(9,500)
Cash dividend payments on common stock	(38,556)	(38,122)
Other	(278)	(2,440)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	(109,137)	(88,810)
Increase in cash and cash equivalents	2,019	(4,307)
Cash and cash equivalents, beginning of period	4,211	9,534
Cash and cash equivalents, end of period	6,230	5,227
Supplemental disclosure of cash flow information: [Abstract]
Interest paid, net of capitalization	23,271	25,264
Income Taxes Paid, Net of refunds	$ (6,900)	$ 10,631