Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Statement Of Financial Position [Abstract]
Available for sale securities, amortized cost	$ 8,898,849	$ 11,822,584
Held to maturity securities, allowance for credit losses	2,045	1,940
Held to Maturity, Fair value	$ 4,393,455	$ 1,442,391
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	80,000,000	80,000,000
Common stock, shares issued	55,056,730	55,056,730
Common stock, shares outstanding	48,403,262	48,430,805
Treasury stock, shares	6,653,468	6,625,925