Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Securities available for sale, amortized cost	$ 6,609,893	$ 5,766,234
Securities held to maturity, fair value	1,455,224	1,467,581
Property and equipment, accumulated depreciation	278,383	271,801
Right of use assets, accumulated amortization	$ 26,291	$ 23,330
Preferred stock, par value per share	$ 20.00	$ 20.00
Common stock, par value per share	$ 3.33	$ 3.33