Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Held to Maturity, Fair value	$ 691,379	$ 304,112
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	49,396,366	45,532,188
Treasury stock, shares	5,660,364	9,524,542