Investments - Narrative (Details) - USD ($)	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]
Cumulative net unamortized unrealized gain	$ 6,342,000		$ 16,865,000
Maximum percentage of shareholders' equity security holdings held of one issuer	10.00%		10.00%
Securities pledged	$ 1,600,000,000		$ 1,700,000,000
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	11,700,000		12,300,000
Allowance for credit losses on held-to-maturity securities	202,000		145,000
Sale of debt securities, available-for-sale	0	$ 9,500,000
Debt Securities, Available-for-Sale, Gain (Loss)		$ 100,000
Other investments, at cost	81,944,000		80,884,000
Reclassified to Held to Maturity
Debt Securities, Available-for-sale [Line Items]
Cumulative net unamortized unrealized gain	6,800,000		7,600,000
Des Moines
Debt Securities, Available-for-sale [Line Items]
Other investments, at cost	$ 10,000,000.0		$ 9,400,000

Accrued interest receivable, held-to-maturity securities

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Mortgage-backed securities, weighted average life

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of unrealized and realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Includes other investments and securities that are not at fair value as of the balance sheet date and those that are not accounted for under the equity method.

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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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