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Investments - Low-Income Housing Tax Credit (LIHTC) Fund Investments (Details)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2024
USD ($)
item
Dec. 31, 2023
USD ($)
item
Dec. 31, 2022
item
Investments, Debt and Equity Securities [Abstract]      
Number of investments in low income housing tax credit fund | item 5 1 2
Investment, book balance $ 13.8 $ 14.4  
Investment, remaining commitments for additional capital contributions 10.1 10.5  
Investment, amortization expense 0.6 0.7  
Investment, tax credit $ 0.3 $ 0.7