Investments - Narrative (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) number_of_securities	Dec. 31, 2018 USD ($) number_of_securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 1,115,323	$ 733,279
Other investments	$ 38,044	$ 26,654
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions \| number_of_securities	73	131
Fair Value	$ 1,135,317	$ 721,369
accumulated other comprehensive income loss available for sale securities adjustment pre tax	6,900
Gross Unrealized Gains	$ 21,548	1,487
Maximum percentage of shareholders' equity security holdings held of one issuer	10.00%
Available-for-sale securities pledged as collateral, fair value	$ 484,800	433,700
Mortgage-backed securities, weighted average life	4 years
Des Moines
Debt Securities, Available-for-sale [Line Items]
Other investments	$ 15,700	$ 9,200
Reclassified to Held to Maturity [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	116,300
Fair Value	123,200
Gross Unrealized Gains	$ 6,800

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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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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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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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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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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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Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

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