Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Held to Maturity, Fair value	$ 991,715	$ 691,379
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	80,000,000	80,000,000
Common stock, shares issued	55,056,730	55,056,730
Common stock, shares outstanding	49,528,986	49,396,366
Treasury stock, shares	5,527,744	5,660,364