v3.26.3
Investments - Narrative (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]          
Cumulative net unamortized unrealized gain $ 311,000   $ 311,000   $ 16,865,000
Maximum percentage of shareholders' equity security holdings held of one issuer 10.00%   10.00%   10.00%
Securities pledged $ 1,700,000,000   $ 1,700,000,000    
Mortgage-backed securities, weighted average life     6 years    
Allowance for credit losses on available-for-sale securities 0   $ 0   $ 0
Accrued interest receivable, held-to-maturity securities 11,300,000   11,300,000   12,300,000
Allowance for credit losses on held-to-maturity securities 165,000   165,000   145,000
Sale of debt and equity securities, available-for-sale 0 $ 0 180,400,000 $ 9,500,000  
Realized gain (loss) on AFS securities     (6,000,000)    
Other investments, at cost $ 120,664,000   120,664,000   80,884,000
Realized gain on sale     4,000,000    
Realized net loss     $ 2,100,000 $ 100,000  
Investment par value (percentage) 50.00%   50.00%    
Minimum investment in capital stock $ 34,000,000.0   $ 34,000,000.0    
Reclassified to Held to Maturity          
Debt Securities, Available-for-sale [Line Items]          
Cumulative net unamortized unrealized gain 5,400,000   5,400,000   7,600,000
Des Moines          
Debt Securities, Available-for-sale [Line Items]          
Other investments, at cost $ 12,900,000   $ 12,900,000   $ 9,400,000