Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cost of available for sale securities	$ 2,248,181	$ 1,893,947
Fair value of held to maturity securities	$ 265,494	$ 274,799
Common stock, par value (in usd per share)	$ 1	$ 1
Common stock, shares authorized	40,000,000	40,000,000
Common stock, shares issued	29,953,356	26,119,929
Treasury stock, shares	0	0
Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized	17,604	17,604
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series A Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, shares authorized	16,000	16,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series C Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized	81,698	81,698
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series D Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized	3,000	3,000
Preferred stock, shares issued	745	1,078
Preferred stock, shares outstanding	745	1,078