Investments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Cumulative net unamortized unrealized gain	$ 5,311,000		$ 1,187,000
Maximum percentage of shareholders' equity security holdings held of one issuer	10.00%		10.00%
Securities pledged	$ 1,500,000,000
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	10,300,000		8,600,000
Allowance for credit losses on held-to-maturity securities	295,000		257,000
Sale of debt securities, available-for-sale	9,500,000	$ 0
Gain on available-for-sale securities	100,000
Other investments, at cost	84,413,000		72,784,000
Reclassified to Held to Maturity
Debt Securities, Available-for-sale [Line Items]
Cumulative net unamortized unrealized gain	10,000,000.0		10,800,000
Des Moines
Debt Securities, Available-for-sale [Line Items]
Other investments, at cost	$ 18,600,000		$ 8,700,000