Investments - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 1,065,223	$ 882,682
Securities available for sale	$ 1,084,223	$ 912,429
Maximum percentage of shareholders' equity security holdings held of one issuer	10.00%	10.00%
Securities pledged	$ 489,400	$ 525,800
Mortgage-backed securities, weighted average life	4 years
Accrued interest receivable, held-to-maturity securities	$ 3,500
Allowance for credit losses on held-to-maturity debt securities	(449)	(449)
Other investments, at cost	50,959	48,764
Des Moines
Debt Securities, Available-for-sale [Line Items]
Other investments, at cost	$ 12,000	$ 10,800