Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2024

Balance Sheet Related Disclosures [Abstract]

Schedule of Inventory

Inventories of materials and supplies, emission allowances, fuel stock and stored natural gas are recorded at average cost and consisted of the following as of March 31, 2024 and December 31, 2023 (dollars in thousands):

	March 31,		December 31,
	2024		2023
Materials and supplies	$	89,956	$	81,651
Emission allowances		60,168		56,097
Stored natural gas		8,289		16,272
Fuel stock		5,296		5,964
Total	$	163,709	$	159,984

Schedule of Other Current Assets

Other current assets consisted of the following as of March 31, 2024 and December 31, 2023 (dollars in thousands):

	March 31,		December 31,
	2024		2023
Prepayments	$	56,222	$	52,752
Income taxes receivable		8,727		29,234
Derivative assets net of collateral		3,597		11,821
Collateral posted for derivative instruments after netting with outstanding    derivatives		4,314		—
Other		10,538		9,977
Total	$	83,398	$	103,784

Schedule of Net Utility Property Recorded at Original Cost Net of Accumulated Depreciation

Net utility property, which is recorded at original cost, net of accumulated depreciation, consisted of the following as of March 31, 2024 and December 31, 2023 (dollars in thousands):

	March 31,		December 31,
	2024		2023
Utility plant in service	$	7,848,978	$	7,799,481
Construction work in progress		195,727		179,527
Total		8,044,705		7,979,008
Less: Accumulated depreciation and amortization		2,296,410		2,278,952
Total	$	5,748,295	$	5,700,056

Other Property and Investments-Net and Other Non-Current Assets

Other property and investments-net and other non-current assets consisted of the following as of March 31, 2024 and December 31, 2023 (dollars in thousands):

	March 31,		December 31,
	2024		2023
Equity investments	$	156,156	$	153,350
Operating lease ROU assets		67,407		67,585
Finance lease ROU assets		35,504		36,414
Non-utility property		33,736		33,813
Notes receivable		15,432		15,287
Long-term prepaid license fees		18,447		19,448
Pension asset		35,853		32,997
Investment in affiliated trust		11,547		11,547
Deferred compensation assets		8,484		7,794
Other		16,131		15,750
Total	$	398,697	$	393,985

Other Current Liabilities

Other current liabilities consisted of the following as of March 31, 2024 and December 31, 2023 (dollars in thousands):

	March 31, 2024		December 31, 2023
Accrued taxes other than income taxes	$	38,452	$	31,928
Derivative liabilities		17,288		17,217
Employee paid time off accruals		33,095		32,072
Accrued interest		41,116		23,539
Climate Commitment Act obligations		—		19,081
Pensions and other postretirement benefits		13,280		14,082
Other		44,329		54,017
Total	$	187,560	$	191,936

Schedule of Other Non-Current Liabilities and Deferred Credits

Other non-current liabilities and deferred credits consisted of the following as of March 31, 2024 and December 31, 2023 (dollars in thousands):

	March 31, 2024		December 31, 2023
Operating lease liabilities	$	64,377	$	63,559
Finance lease liabilities		38,204		39,095
Deferred investment tax credits		28,033		28,233
Climate Commitment Act obligations		60,701		26,026
Asset retirement obligations		18,175		18,058
Derivative liabilities		4,773		17,902
Other		19,099		17,357
Total	$	233,362	$	210,230

Schedule of Regulatory Assets and Liabilities

Regulatory assets and liabilities consisted of the following as of March 31, 2024 and December 31, 2023 (dollars in thousands):

	March 31, 2024				December 31, 2023
	Current		Non-Current		Current		Non-Current
Regulatory Assets
Energy commodity derivatives	$	29,868	$	4,458	$	51,419	$	17,720
Decoupling surcharge		5,791		3,637		4,638		5,469
Deferred natural gas costs		24,013		—		60,667		—
Deferred power costs		24,420		18,261		29,190		20,654
Deferred income taxes		—		245,260		—		244,303
Pension and other postretirement benefit plans		—		116,658		—		117,658
Interest rate swaps		—		177,563		—		179,489
AFUDC above FERC allowed rate		—		49,317		—		49,985
Settlement with Coeur d'Alene Tribe		—		36,413		—		36,692
Advanced meter infrastructure		—		28,586		—		29,345
Utility plant abandoned		—		36,774		—		38,274
Deferred Climate Commitment Act costs		—		61,491		—		46,022
COVID-19 deferrals		—		12,044		—		12,142
Unamortized debt repurchase costs		—		5,584		—		5,701
Demand side management programs		—		10,407		—		10,033
Other regulatory assets		498		81,168		413		80,681
Total regulatory assets	$	84,590	$	887,621	$	146,327	$	894,168
Regulatory Liabilities
Other income tax related liabilities	$	18,436	$	55,264	$	25,129	$	56,582
Excess deferred income taxes		14,240		289,738		14,510		293,029
Deferred natural gas costs		8,916		—		9,296		—
Deferred power costs		—		1,631		—		4,000
Decoupling rebate		12,544		9,205		18,680		6,344
Utility plant retirement costs		—		424,807		—		417,027
Interest rate swaps		—		24,559		—		23,752
Deferred Climate Commitment Act revenues		—		41,775		—		37,231
COVID-19 deferrals		—		9,744		—		10,172
Other regulatory liabilities		8,543		7,938		8,392		8,529
Total regulatory liabilities	$	62,679	$	864,661	$	76,007	$	856,666