CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Securities carried at fair value, cost	$ 4,869,531	$ 3,311,433
Allowance for Credit Losses	61	0
Estimated Fair Value	$ 99,619	$ 100,484
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	60,000,000	60,000,000
Common stock, shares issued (in shares)	36,885,390	36,704,278
Obligations of states and political subdivisions
Allowance for Credit Losses	$ 61	$ 0
Estimated Fair Value	$ 99,619	$ 100,484
Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	6,104	6,104
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Series A Junior Participating preferred stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	16,000	16,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Series B Fixed Rate Cumulative Perpetual Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	81,698	81,698
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Series C Senior Non-Cumulative Perpetual Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	81,698	81,698
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Series D Senior Non-Cumulative Perpetual Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	3,000	3,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Series E Fixed-Rate Reset Cumulative Perpetual Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	11,500	0
Preferred stock, shares issued (in shares)	11,500	0
Preferred stock, shares outstanding (in shares)	11,500	0