Investments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Cumulative net unamortized unrealized gain	$ 588		$ 1,603
Maximum percentage of shareholders' equity security holdings held of one issuer	10.00%		10.00%
Securities pledged	$ 1,200,000		$ 1,600,000
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	7,100		6,500
Allowance for credit losses on held-to-maturity securities	350		785
Sale of debt securities, available-for-sale	0	$ 28,400
Debt Securities, Available-for-sale, Realized Gain		$ 400
Other investments, at cost	74,077		66,195
Reclassified to Held to Maturity
Debt Securities, Available-for-sale [Line Items]
Cumulative net unamortized unrealized gain	13,300		14,100
Des Moines
Debt Securities, Available-for-sale [Line Items]
Other investments, at cost	$ 14,300		$ 7,800