CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Securities held-to-maturity, fair value	$ 1,033,749,000	$ 1,066,531,000
Allowance for credit losses - securities held-to-maturity	$ (198,000)	$ (191,000)
Preferred stock, par value (in dollars per share)	$ 0	$ 0
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	225,000	225,000
Preferred stock, shares outstanding (in shares)	225,000	225,000
Preferred Stock, Liquidation Preference Per Share	$ 1,000	$ 1,000
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	180,000,000	180,000,000
Common stock, shares issued (in shares)	76,088,000	75,850,000
Common stock, shares outstanding (in shares)	76,088,000	75,850,000