CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Available for sale securities, amortized cost	$ 211,990	$ 234,252
Held-to-maturity securities, fair value	$ 499,885	$ 260,139
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares, outstanding	6,965,557	6,926,728