Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investment in marketable equity securities at cost	$ 84,297	$ 84,837
Investment securities available for sale at cost	7,270,552	6,911,965
Investment securities held to maturity at fair value	$ 2,774,982	$ 2,838,499
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	345,000	345,000
Preferred stock, shares outstanding	345,000	345,000
Class A Common Stock
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized	16,000,000	16,000,000
Common stock, shares issued	8,811,220	8,811,220
Common stock, shares outstanding	8,811,220	8,811,220
Class B Common Stock
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized	2,000,000	2,000,000
Common stock, shares issued	1,005,185	1,005,185
Common stock, shares outstanding	1,005,185	1,005,185