CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Securities held-to-maturity, fair value	$ 1,051,091	$ 201,217
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)	0	0
Preferred stock, shares outstanding (in shares)	0	0
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)	75,800,000	76,564,000
Common stock, shares outstanding (in shares)	75,800,000	76,564,000