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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2023
Accounting Policies [Abstract] |
Summary of Ratio of Depreciation to Average Depreciable Property and Average Service Lives for Utility Plan in Service | For utility operations, the ratio of depreciation provisions to average depreciable property was as follows for the years ended December 31:
|  | 2023 |  |  | 2022 |  |  | 2021 |
Avista Utilities |  |  | 3.52 | % |  |  | 3.50 | % |  |  | 3.54 | %
Alaska Electric Light and Power Company |  |  | 2.78 | % |  |  | 2.78 | % |  |  | 2.77 | %
The average service lives for the following broad categories of utility plant in service are (in years):
|  | Avista Utilities |  |  | Alaska Electric Light and Power Company |
Electric thermal/other production |  |  | 26 |  |  |  | 41 |
Hydroelectric production |  |  | 79 |  |  |  | 42 |
Electric transmission |  |  | 50 |  |  |  | 43 |
Electric distribution |  |  | 40 |  |  |  | 39 |
Natural gas distribution property |  |  | 44 |  |  | N/A |
Other shorter-lived general plant |  |  | 8 |  |  |  | 18 |
The gross balances of the major classifications of property, plant and equipment are detailed in the following table as of December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |
Avista Utilities: |  |  |  |  |  |
Electric production |  | $ | 1,498,398 |  |  | $ | 1,593,795 |
Electric transmission |  |  | 1,059,389 |  |  |  | 994,709 |
Electric distribution |  |  | 2,383,201 |  |  |  | 2,236,376 |
Electric construction work-in-progress (CWIP) and other |  |  | 394,711 |  |  |  | 376,981 |
Electric total |  |  | 5,335,699 |  |  |  | 5,201,861 |
Natural gas underground storage |  |  | 59,994 |  |  |  | 58,072 |
Natural gas distribution |  |  | 1,539,467 |  |  |  | 1,452,637 |
Natural gas CWIP and other |  |  | 91,492 |  |  |  | 88,264 |
Natural gas total |  |  | 1,690,953 |  |  |  | 1,598,973 |
Common plant (including CWIP) |  |  | 759,498 |  |  |  | 744,173 |
Total Avista Utilities |  |  | 7,786,150 |  |  |  | 7,545,007 |
AEL&P: |  |  |  |  |  |
Electric production |  |  | 118,817 |  |  |  | 106,390 |
Electric transmission |  |  | 22,827 |  |  |  | 22,856 |
Electric distribution |  |  | 32,322 |  |  |  | 29,269 |
Electric CWIP and other |  |  | 8,552 |  |  |  | 12,295 |
Electric total |  |  | 182,518 |  |  |  | 170,810 |
Common plant |  |  | 10,340 |  |  |  | 10,018 |
Total AEL&P |  |  | 192,858 |  |  |  | 180,828 |
Total gross utility property |  |  | 7,979,008 |  |  |  | 7,725,835 |
Other (1) |  |  | 6,425 |  |  |  | 16,631 |
Total |  | $ | 7,985,433 |  |  | $ | 7,742,466 |
(1) Included in other property and investments-net and other non-current assets on the Consolidated Balance Sheets. Accumulated depreciation was less than $0.1 million as of December 31, 2023 and $2.4 million as of December 31, 2022 for the other businesses.
Summary of Effective AFUDC Rate | The effective AFUDC rate was the following for the years ended December 31:
|  | 2023 |  |  | 2022 |  |  | 2021 |
Avista Utilities |  |  | 7.03 | % |  |  | 7.12 | % |  |  | 7.19 | %
Alaska Electric Light and Power Company |  |  | 8.61 | % |  |  | 8.08 | % |  |  | 8.90 | %
Stock-Based Compensation | The Company recorded stock-based compensation expense (included in other operating expenses) and income tax benefits in the Consolidated Statements of Income of the following amounts for the years ended December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |  |  | 2021 |
Stock-based compensation expense |  | $ | 7,144 |  |  | $ | 7,567 |  |  | $ | 4,713 |
Income tax benefits |  |  | 1,500 |  |  |  | 1,589 |  |  |  | 990 |
Excess tax benefits (expenses) on settled share-based employee payments |  |  | 84 |  |  |  | (19 | ) |  |  | (909 | )
The following table summarizes the number of grants, vested and unvested shares, earned shares (based on market metrics), and other pertinent information related to the Company's stock compensation awards for the years ended December 31:
|  | 2023 |  |  | 2022 |  |  | 2021 |
Restricted Shares |  |  |  |  |  |  |  |  |
Shares granted during the year |  |  | 76,806 |  |  |  | 115,746 |  |  |  | 62,594 |
Shares vested during the year |  |  | 75,007 |  |  |  | 44,829 |  |  |  | 34,854 |
Unvested shares at end of year |  |  | 152,140 |  |  |  | 157,860 |  |  |  | 96,127 |
Unrecognized compensation expense at end of year (in thousands) |  | $ | 3,477 |  |  | $ | 3,923 |  |  | $ | 2,215 |
TSR Awards |  |  |  |  |  |  |  |  |
TSR shares granted during the year |  |  | 34,912 |  |  |  | 69,814 |  |  |  | 64,910 |
TSR shares vested during the year |  |  | 61,456 |  |  |  | 43,730 |  |  |  | 77,174 |
TSR shares earned based on market metrics |  |  | 44,863 |  |  |  | 48,890 |  |  |  | 58,652 |
Unvested TSR shares at end of year |  |  | 96,915 |  |  |  | 130,567 |  |  |  | 107,854 |
Unrecognized compensation expense at end of year (in thousands) |  | $ | 2,235 |  |  | $ | 3,533 |  |  | $ | 2,653 |
CEPS Awards |  |  |  |  |  |  |  |  |
CEPS shares granted during the year |  |  | 104,685 |  |  |  | 69,814 |  |  |  | 64,910 |
CEPS shares vested during the year |  |  | 61,456 |  |  |  | 43,730 |  |  |  | 38,590 |
CEPS shares earned based on performance metrics |  |  | 33,801 |  |  |  | — |  |  |  | 26,627 |
Unvested CEPS shares at end of year |  |  | 161,235 |  |  |  | 130,567 |  |  |  | 107,854 |
Unrecognized compensation expense at end of year (in thousands) |  | $ | 2,439 |  |  | $ | 2,471 |  |  | $ | 1,223 |
Other Expense (Income) - Net | Other income - net consisted of the following items for the years ended December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |  |  | 2021 |
Interest income |  | $ | 5,949 |  |  | $ | 1,957 |  |  | $ | 1,943 |
Interest on regulatory deferrals |  |  | 8,713 |  |  |  | 1,914 |  |  |  | 1,206 |
Equity-related AFUDC |  |  | 6,886 |  |  |  | 6,704 |  |  |  | 7,004 |
Non-service portion of pension and other postretirement benefit expenses |  |  | 630 |  |  |  | 3,037 |  |  |  | (1,386 | )
Earnings (losses) on investments |  |  | (3,227 | ) |  |  | 48,492 |  |  |  | 21,402 |
Other income |  |  | 575 |  |  |  | 613 |  |  |  | 3,129 |
Total |  | $ | 19,526 |  |  | $ | 62,717 |  |  | $ | 33,298 |
Allowance for Doubtful Accounts | The following table presents the activity in the allowance for doubtful accounts during the years ended December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |  |  | 2021 |
Allowance as of the beginning of the year |  | $ | 6,473 |  |  | $ | 10,465 |  |  | $ | 11,387 |
Additions expensed during the year |  |  | 6,865 |  |  |  | 149 |  |  |  | 9,279 |
Net deductions (1) |  |  | (8,351 | ) |  |  | (4,141 | ) |  |  | (10,201 | )
Allowance as of the end of the year |  | $ | 4,987 |  |  | $ | 6,473 |  |  | $ | 10,465 |
(1) The higher balance in 2021 is related to COVID-19 forgiveness program. The Company received support from various government agencies in 2023 and 2022 in the amounts of $1.5 million and $6.1 million, respectively, which were applied to overdue customer accounts.
Estimated Retirement Costs Collected from Customers | The Company records the amount of estimated retirement costs collected from customers (that do not represent legal or contractual obligations) and includes them as a non-current regulatory liability on the Consolidated Balance Sheets in the following amounts as of December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |
Regulatory liability for utility plant retirement costs |  | $ | 417,027 |  |  | $ | 376,817 |
Summary of Appropriated Retained Earnings Amount Included in Retained Earnings | The appropriated retained earnings amounts included in retained earnings were as follows as of December 31 (dollars in thousands):
|  | 2023 |  |  | 2022 |
Appropriated retained earnings |  | $ | 59,118 |  |  | $ | 57,231 |

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