Investments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 930,454		$ 882,682
Securities available for sale	$ 945,660		$ 912,429
Maximum percentage of shareholders' equity security holdings held of one issuer	10.00%		10.00%
Securities pledged	$ 465,900		$ 525,800
Mortgage-backed securities, weighted average life	3 years
Accrued interest receivable, held-to-maturity securities	$ 3,500
Allowance for credit losses on held-to-maturity debt securities	449		449
Proceeds from sales		$ 207
Gross gains realized		$ 4
Other investments, at cost	51,099		48,764
Des Moines
Debt Securities, Available-for-sale [Line Items]
Other investments, at cost	$ 12,000		$ 10,800

Accrued interest receivable, held-to-maturity securities

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Maximum percentage of shareholders' equity security holdings held of one issuer.

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Mortgage-backed securities, weighted average life

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Amortized cost 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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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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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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Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

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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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