Consolidated Balance Sheet Statement Parenthetical - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investment securities available for sale at amortized cost	$ 1,283,161	$ 1,084,105
Investment securities held to maturity at fair value	$ 92,604	$ 116,384
Preferred Stock, Par Value Per Share	$ 1.00	$ 1.00
Preferred Stock, Shares Authorized	2,000,000	2,000,000
Common Stock, Par Value Per Share	$ 1.00	$ 1.00
Common Stock, Shares Authorized	170,000,000	170,000,000
Common Stock, Shares, Issued	83,731,769	83,410,961
Common Stock, Shares, Outstanding	83,731,769	83,410,961
Series D Preferred Stock [Member]
Preferred Stock, Par Value Per Share	$ 1.00
Preferred Stock, Shares Issued	50,000	50,000
Preferred Stock, Shares Outstanding	50,000	50,000
Preferred Stock, Liquidation Preference Per Share	$ 1,000	$ 1,000