Consolidated Balance Sheets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment:
Utility Plant, at original cost	$ 2,424,134	$ 2,211,239
Accumulated Depreciation	(471,222)	(440,473)
Nonutility Property and Equipment, at cost	821,942	785,646
Accumulated Depreciation	(151,084)	(108,307)
Property, Plant and Equipment - Net	2,623,770	2,448,105
Investments:
Available-for-Sale Securities	32	14,810
Restricted Investments	13,628	48,758
Investment in Affiliates	28,906	16,983
Total Investments	42,566	80,551
Current Assets:
Cash and Cash Equivalents	18,282	3,877
Accounts Receivable	222,339	178,359
Unbilled Revenues	59,680	40,044
Provision for Uncollectibles	(12,744)	(10,252)
Notes Receivable	1,454	11,800
Notes Receivable - Affiliate	2,461	3,134
Natural Gas in Storage, average cost	53,857	54,211
Materials and Supplies, average cost	6,753	5,088
Prepaid Taxes	17,471	21,753
Derivatives - Energy Related Assets	72,391	83,093
Other Prepayments and Current Assets	31,369	40,167
Total Current Assets	473,313	431,274
Regulatory and Other Noncurrent Assets:
Regulatory Assets	410,746	323,434
Derivatives - Energy Related Assets	8,502	16,238
Notes Receivable - Affiliate	13,275	13,275
Contract Receivables	29,037	28,609
Notes Receivable	25,271	35,439
Goodwill	4,838	8,880
Identifiable Intangible Assets	15,820	21,553
Other	83,429	64,575
Total Regulatory and Other Noncurrent Assets	590,918	512,003
Total Assets	3,730,567	3,471,933
Common Stock: Par Value $1.25 per share; Authorized 120,000,000 shares; Outstanding Shares: 79,478,055 (2016) and 70,965,622 (2015)
Balance at Beginning of Year	88,707	85,418
Common Stock Issued or Granted Under Stock Plans	10,640	3,289
Balance at End of Year	99,347	88,707
Premium on Common Stock	706,943	499,460
Treasury Stock (at par)	(266)	(296)
Accumulated Other Comprehensive Loss	(27,381)	(24,499)
Retained Earnings	510,597	474,167
Total Equity	1,289,240	1,037,539
Long-term Debt, Excluding Current Maturities	808,005	997,427
Total Capitalization	2,097,245	2,034,966
Current Liabilities:
Notes Payable	296,100	431,700
Current Portion of Long-Term Debt	231,909	29,454
Accounts Payable	243,669	186,400
Customer Deposits and Credit Balances	48,068	20,146
Environmental Remediation Costs	46,120	50,559
Taxes Accrued	2,082	2,336
Derivatives - Energy Related Liabilities	60,082	90,708
Derivatives - Other	681	0
Interest Accrued	6,231	7,316
Pension Benefits	2,463	2,261
Other Current Liabilities	15,219	11,596
Total Current Liabilities	952,624	832,476
Deferred Credits and Other Noncurrent Liabilities:
Deferred Income Taxes - Net	343,549	295,945
Pension and Other Postretirement Benefits	95,235	76,068
Environmental Remediation Costs	108,893	76,064
Asset Retirement Obligations	59,427	57,943
Derivatives - Energy Related Liabilities	4,540	21,697
Derivatives - Other	9,349	10,943
Regulatory Liabilities	49,121	42,841
Other	10,584	22,990
Total Deferred Credits and Other Noncurrent Liabilities	680,698	604,491
Commitments and Contingencies (Note 15)
Total Capitalization and Liabilities	$ 3,730,567	$ 3,471,933