Consolidated Statements of Financial Position (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Held-to-maturity, fair value	$ 618,672	$ 662,906
Preferred stock, no par value (in dollars per share)	$ 0	$ 0
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	0	0
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized	135,000,000	135,000,000
Common stock, shares issued	71,460,119	71,207,114
Common stock, shares outstanding	71,460,119	71,207,114