Investments - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Cumulative net unamortized unrealized gain		$ 8,000		$ 8,000		$ 481,000
Maximum percentage of shareholders' equity security holdings held of one issuer		10.00%		10.00%		10.00%
Securities pledged		$ 1,400,000,000		$ 1,400,000,000		$ 734,500,000
Mortgage-backed securities, weighted average life				5 years
Provision for credit losses on available-for-sale securities				$ 5,000,000
Charge-off				5,000,000
Allowance for credit losses on available-for-sale securities		0		0		0
Accrued interest receivable, held-to-maturity securities		6,700,000		6,700,000		5,800,000
Allowance for credit losses on held-to-maturity securities		785,000		785,000		735,000
Sale of debt securities, available-for-sale	$ 28,400,000	0	$ 0	28,741,000	$ 0
Debt Securities, Available-for-sale, Realized Gain	$ 400,000
Other investments, at cost		61,819,000		61,819,000		63,790,000
Reclassified to Held to Maturity
Debt Securities, Available-for-sale [Line Items]
Cumulative net unamortized unrealized gain		15,000,000		15,000,000		17,600,000
Des Moines
Debt Securities, Available-for-sale [Line Items]
Other investments, at cost		$ 10,000,000		$ 10,000,000		$ 14,000,000