Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Consolidated Balance Sheets [Abstract]
Securities available for sale, amortized cost	$ 2,755,806	$ 2,949,057
Securities held to maturity, fair value	2,935,856	2,962,010
Property and equipment, accumulated depreciation	$ 225,969	$ 214,998
Preferred stock, par value per share	$ 20.00	$ 20.00
Common stock, par value per share	$ 3.33	$ 3.33