Unaudited Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 13,126	$ 20,502
Restricted Cash and Cash Equivalents	5	6,120
Accounts Receivable, after Allowance for Credit Loss, Current	177,636	165,193
Accounts Receivable, Allowance for Credit Loss, Current	1,100	3,155
Inventory, Net	76,362	95,506
Regulatory assets	84,736	45,430
Income Taxes Receivable, Current	26,954	24,384
Other Assets, Current	48,555	17,842
Total current assets	427,374	374,977
UTILITY PLANT:
Property, Plant and Equipment, Gross	6,615,484	6,530,395
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	2,624,804	2,643,695
Utility plant in service - net	3,990,680	3,886,700
Construction in Progress, Gross	169,464	209,584
Total net property, plant and equipment	4,160,144	4,096,284
Other Assets, Noncurrent [Abstract]
Intangible Assets, Net (Excluding Goodwill)	59,640	59,141
Regulatory assets	364,975	392,801
Other Assets, Miscellaneous, Noncurrent	55,661	46,716
Total other non-current assets	480,276	498,658
TOTAL ASSETS	5,067,794	4,969,919
CURRENT LIABILITIES:
Debt, Current	135,000	169,907
Accounts payable	165,871	127,089
Accrued taxes	29,652	26,620
Interest Payable, Current	42,602	31,733
Customer deposits	28,511	27,929
Regulatory Liability, Current	7,427	30,036
Accrued Liabilities and Other Liabilities	35,887	19,453
Total current liabilities	444,950	432,767
NON-CURRENT LIABILITIES:
Long-term debt (Note 4)	2,651,560	2,556,278
Deferred income tax liabilities	295,942	275,714
Taxes Payable	7,401	7,458
Regulatory Liability, Noncurrent	828,803	839,360
Accrued pension and other postretirement benefits	5,472	5,334
Asset retirement obligations	191,996	195,236
Derivative Liability, Noncurrent	44,816	63,215
Other non-current liabilities	389	13,785
Total non-current liabilities	4,026,379	3,956,380
Liabilities	4,471,329	4,389,147
Common shareholders' equity:
Additional Paid in Capital	580,855	588,966
Accumulated Other Comprehensive Income (Loss), Net of Tax	(27,337)	(43,420)
Accumulated deficit	(16,837)	(24,558)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	536,681	520,988
Cumulative preferred stock of subsidiary	59,784	59,784
Total common shareholders' equity	596,465	580,772
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 5,067,794	$ 4,969,919