XML 41 R31.htm IDEA: XBRL DOCUMENT v3.22.1
Investments - Narrative (Details) - USD ($)
 3 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]      
Debt Securities, Available-for-sale, Amortized Cost $ 1,491,748,000   $ 1,358,960,000
Cumulative net unamortized unrealized gain $ 1,263,000   15,247,000
Maximum percentage of shareholders' equity security holdings held of one issuer 10.00%    
Securities pledged $ 581,400,000   752,700,000
Mortgage-backed securities, weighted average life 5 years    
Allowance for credit losses on available-for-sale securities $ 0   0
Accrued interest receivable, held-to-maturity securities 4,100,000   3,400,000
Allowance for credit losses on held-to-maturity debt securities (558,000)   (614,000)
Sale of debt securities, available-for-sale 0 $ 0  
Other investments, at cost 60,444,000   59,896,000
Reclassified to Held to Maturity      
Debt Securities, Available-for-sale [Line Items]      
Debt Securities, Available-for-sale, Amortized Cost 116,900,000    
Cumulative net unamortized unrealized gain 20,300,000   21,000,000
Des Moines      
Debt Securities, Available-for-sale [Line Items]      
Other investments, at cost $ 12,000,000   $ 12,100,000