Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Debt securities available-for-sale at amortized cost	$ 1,150,224	$ 978,774
Shareholders' equity:
Preferred stock, shares authorized (in shares)	300,000	300,000
Common stock, par value (in dollars per share)	$ 5.00	$ 5.00
Common stock, shares authorized (in shares)	25,000,000	25,000,000
Common stock, shares outstanding (in shares)	17,826,076	17,810,401