Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Securities available for sale, amortized cost	$ 4,698,304	$ 4,637,610
Securities held to maturity, fair value	1,553,593	1,611,004
Property and equipment, accumulated depreciation	259,784	249,527
Right of use assets, accumulated amortization	$ 17,649	$ 12,194
Preferred stock, par value per share	$ 20.00	$ 20.00
Common stock, par value per share	$ 3.33	$ 3.33