| December 31, 2023 | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Significant Other Observable Inputs (Level 2) | Significant Unobservable Inputs (Level 3) | Margin Cash Collateral Offset | Total Net Fair Value | ||||||||||||||||||||||||||||||||||||||||||||||
| (in thousands) | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Restricted cash equivalents | $ | 14,996 | $ | — | $ | — | $ | — | $ | 14,996 | Rabbi trust investments | 17,093 | — | — | — | 17,093 | Total | $ | 32,089 | $ | — | $ | — | $ | — | $ | 32,089 | December 31, 2022 | |||||||||||||||||||||||
| Restricted cash equivalents | $ | 12,990 | $ | — | $ | — | $ | — | $ | 12,990 | Rabbi trust investments | 20,895 | — | — | — | 20,895 | Total | $ | 33,885 | $ | — | $ | — | $ | — | $ | 33,885 | ||||||||||||||||||||||||
| Year Ended December 31, 2023 vs. 2022 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Income Before Income Taxes | Income Tax Benefit (Expense) | Net Income | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| (in millions) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Year ended December 31, 2022 | $ | 182.4 | $ | 0.6 | $ | 183.0 | Variance in revenue and fuel, purchased supply, and direct transmission expense(1) items impacting net income: | Montana rate review - new base rates | 32.6 | (8.3) | 24.3 | Lower non-recoverable Montana electric supply costs | 14.2 | (3.6) | 10.6 | Montana property tax tracker collections | 12.8 | (3.2) | 9.6 | Higher Montana natural gas transportation | 2.2 | (0.6) | 1.6 | Higher electric transmission revenue | 0.6 | (0.2) | 0.4 | Lower natural gas retail volumes | (7.0) | 1.8 | (5.2) | Lower electric retail volumes | (1.8) | 0.5 | (1.3) | Higher revenue from lower production tax credits, offset within income tax benefit (expense) | 3.8 | (3.8) | — | Other | (1.7) | 0.4 | (1.3) | Variance in expense items(2) impacting net income: | Higher depreciation expense | (15.5) | 3.9 | (11.6) | Higher interest expense | (14.5) | 3.7 | (10.8) | Higher operating, maintenance, and administrative expenses | (14.4) | 3.6 | (10.8) | Lower property and other taxes not recoverable within trackers | 3.0 | (0.8) | 2.2 | Other | 4.9 | (1.5) | 3.4 | Year ended December 31, 2023 | $ | 201.6 | $ | (7.5) | $ | 194.1 | Change in Net Income | $ | 11.1 | |||||||||||||||||||||||
