Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Debt securities held-to-maturity, fair value	$ 287,904	$ 268,803
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, authorized (in shares)	150,000,000	150,000,000
Common stock, issued (in shares)	79,013,729	79,234,077
Common stock, outstanding (in shares)	79,013,729	79,234,077
Common stock issuable (in shares)	664,640	674,499