Statements of Consolidated Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows from Operating Activities:
Net Income	$ 118,810	$ 105,107	$ 97,046
Loss from Discontinued Operations	251	503	582
Income from Continuing Operations	119,061	105,610	97,628
Adjustments to Reconcile Income from Continuing Operations to Net Cash Provided by Operating Activities:
Depreciation and Amortization	109,818	91,042	78,511
Net Unrealized (Gain) Loss on Derivatives - Energy Related	(26,935)	(8,401)	6,592
Unrealized (Gain) Loss on Derivatives - Other	(647)	(96)	467
Provision for Losses on Accounts Receivable	6,907	14,730	9,519
CIP Receivable/Payable	(24,943)	(7,324)	15,226
Deferred Gas Costs - Net of Recoveries	11,753	28,648	(44,976)
Deferred SBC Costs - Net of Recoveries	(7,102)	9,557	11,048
Stock-Based Compensation Expense	3,892	2,213	1,893
Deferred and Noncurrent Income Taxes - Net	55,789	3,861	1,670
Environmental Remediation Costs - Net	(39,731)	(22,057)	(8,265)
Gas Plant Cost of Removal	(6,070)	(5,096)	(4,848)
Pension Contribution	0	(15,000)	0
Changes in:
Accounts Receivable	(67,160)	92,624	(14,323)
Inventories	387	9,226	(4,787)
Prepaid and Accrued Taxes - Net	4,253	(9,091)	(5,822)
Accounts Payable and Other Accrued Liabilities	112,199	(103,410)	27,429
Derivatives - Energy Related	6,723	(8,069)	169
Other Assets and Liabilities	4,090	8,860	(5,444)
Cash Flows from Discontinued Operations	(44)	(1,033)	(355)
Net Cash Provided by Operating Activities	262,240	186,794	161,332
Cash Flows from Investing Activities:
Capital Expenditures	(278,002)	(345,621)	(342,578)
Purchase of Available for Sale Securities	0	(6,059)	0
Proceeds from Restricted Investments	1,738	0	0
Proceeds from Sale of Property, Plant and Equipment	0	0	53
Net Proceeds from (Purchase of) Restricted Investments in Margin Accounts	31,971	20,069	(22,337)
Net Sale of Restricted Investments from Escrowed Loan Proceeds	0	101	0
Investment in Long-Term Receivables	(10,886)	(19,033)	(13,024)
Proceeds from Long-Term Receivables	10,014	8,769	6,544
Notes Receivable	9,916	(9,916)	0
Purchase of Company-Owned Life Insurance	(2,398)	(2,328)	(1,250)
Acquisition of Subsidiary, Net of Cash Acquired	0	1,394	0
Investment in Affiliate	(12,943)	(20,229)	0
Return of Investment in Affiliate	4,750	0	0
Advances on Notes Receivable - Affiliate	0	(2,075)	(7,521)
Net Repayment of Notes Receivable - Affiliate	672	4,276	5,094
Net Cash Used in Investing Activities	(245,168)	(370,652)	(375,019)
Cash Flows from Financing Activities:
Net (Repayments of) Borrowings from Short-Term Credit Facilities	(135,600)	186,000	(108,200)
Proceeds from Issuance of Long-Term Debt	61,000	130,000	329,000
Payments for Issuance of Long-Term Debt	(147)	(64)	(2,184)
Principal Repayments of Long-Term Debt	(49,366)	(125,009)	(21,000)
Dividends on Common Stock	(82,380)	(70,158)	(63,869)
Proceeds from Sale of Common Stock	214,426	63,192	80,680
Payment of Lease Obligation	(10,600)	0	0
Other	0	(397)	(387)
Net Cash (Used in) Provided by Financing Activities	(2,667)	183,564	214,040
Net Increase (Decrease) in Cash and Cash Equivalents	14,405	(294)	353
Cash and Cash Equivalents at Beginning of Year	3,877	4,171	3,818
Cash and Cash Equivalents at End of Year	18,282	3,877	4,171
Cash paid during the year for:
Interest (Net of Amounts Capitalized)	32,372	30,915	28,854
Income Taxes (Net of Refunds)	194	1,828	6,858
Supplemental Disclosures of Non-Cash Investing Activities
Capital Expenditures acquired on account but unpaid as of year-end	39,130	51,433	36,491
Notes Receivable from Affiliate Exchanged for Notes Receivable from a Third Party	0	16,389	0
Notes Receivable Exchanged for Accounts Payable	$ 10,168	$ 0	$ 0