Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amortized cost	$ 282,273	$ 260,924
Held-to-maturity securities, fair value	2,579,103	2,361,304
Equity securities, amortized cost	$ 1,635	$ 1,635
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	100,000	100,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A Common Stock [Member]
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	3,655,469	3,650,949
Class B Common Stock [Member]
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	5,000,000	5,000,000
Common stock, shares issued	1,912,440	1,916,960