Consolidated Statement of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities: [Abstract]
Net Income	$ 36,641	$ 28,486
Adjustments to reconcile net income to cash provided by operations: [Abstract]
Depreciation and amortization	20,394	20,111
Regulatory amortization of gas reserves	4,075	5,255
Deferred Tax Liabilities, net	23,353	5,918
Qualified defined benefit pension plan expense	1,311	1,509
Contributions to qualified defined benefit pension plans	(2,900)	(2,630)
Deferred environmental (expenditures) recoveries, net of recoveries	(2,665)	(3,315)
Regulatory disallowance of prior environmental cost deferrals	3,273	15,000
Interest income on deferred environmental expenses	0	(5,322)
Amortization of environmental remediation	5,029	0
Other	1,169	900
Changes in assets and liabilities: [Abstract]
Receivables, net	22,242	29,193
Inventories	10,115	8,543
Taxes Accrued	7,729	6,724
Accounts payable	(14,537)	(26,550)
Interest accrued	3,798	4,348
Deferred gas costs	8,519	13,074
Other, net	18,592	17,005
Net Cash Provided by (Used in) Operating Activities, Continuing Operations	146,138	118,249
Payments to Acquire Property, Plant, and Equipment [Abstract]
Capital expenditures	(30,054)	(27,135)
Other	24	(1,811)
Net Cash Provided by (Used in) Investing Activities, Continuing Operations	(30,030)	(28,946)
Financing activities: [Abstract]
Common Stock Issued, net	1,999	700
Change in short-term debt	(105,135)	(78,500)
Cash dividend payments on common stock	(12,823)	(12,688)
Other	(39)	(3,131)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	(115,998)	(93,619)
Increase in cash and cash equivalents	110	(4,316)
Cash and cash equivalents, beginning of period	4,211	9,534
Cash and cash equivalents, end of period	4,321	5,218
Supplemental disclosure of cash flow information: [Abstract]
Interest paid, net of capitalization	5,232	5,399
Income Taxes Paid, Net of refunds	$ (7,900)	$ 0