Consolidated Statement of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities: [Abstract]
Net Income	$ 38,660	$ 30,683
Adjustments to reconcile net income to cash provided by operations: [Abstract]
Depreciation and amortization	40,807	40,341
Regulatory amortization of gas reserves	7,647	10,023
Deferred Tax Liabilities, net	27,022	6,886
Qualified defined benefit pension plan expense	2,737	3,032
Contributions to qualified defined benefit pension plans	(6,120)	(5,810)
Deferred environmental (expenditures) recoveries, net of recoveries	(5,521)	(5,659)
Regulatory disallowance of prior environmental cost deferrals	3,273	15,000
Interest income on deferred environmental expenses	0	(5,322)
Amortization of environmental remediation	6,922	0
Other	2,121	418
Changes in assets and liabilities: [Abstract]
Receivables, net	87,271	85,121
Inventories	4,525	1,321
Taxes Accrued	3,710	(249)
Accounts payable	(17,141)	(37,532)
Interest accrued	(80)	(157)
Deferred gas costs	(9,295)	21,718
Other, net	13,022	7,670
Net Cash Provided by (Used in) Operating Activities, Continuing Operations	199,560	167,484
Payments to Acquire Property, Plant, and Equipment [Abstract]
Capital expenditures	(62,153)	(58,072)
Utility gas reserves	0	1,945
Restricted cash	0	1,500
Other	2,453	201
Net Cash Provided by (Used in) Investing Activities, Continuing Operations	(59,700)	(61,316)
Financing activities: [Abstract]
Common Stock Issued, net	4,332	812
Long-term debt retired	0	40,000
Change in short-term debt	(117,235)	(44,400)
Cash dividend payments on common stock	(25,677)	(25,398)
Other	(28)	(2,250)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	(138,608)	(111,236)
Increase in cash and cash equivalents	1,252	(5,068)
Cash and cash equivalents, beginning of period	4,211	9,534
Cash and cash equivalents, end of period	5,463	4,466
Supplemental disclosure of cash flow information: [Abstract]
Interest paid, net of capitalization	18,124	19,615
Income Taxes Paid, Net of refunds	$ (7,900)	$ 4,625