CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Series D Preferred Stock	Preferred Stock	Preferred Stock Series D Preferred Stock	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Balance at beginning of period at Dec. 31, 2016	$ 740,916		$ 1,357		$ 26,120	$ 328,376	$ 416,109	$ (31,046)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	71,628						61,600	10,028
Cash dividends declared:
Preferred	(45)						(45)
Common	(9,108)						(9,108)
Conversion of Series D preferred stock		$ (419)		$ (419)
Purchase of shares of common stock	(440)								(440)
Issuance of shares of common stock	175,564				3,826	171,298			440
Stock based compensation	3,588					3,588
Balance at end of period at Sep. 30, 2017	981,684		938		29,946	503,262	468,556	(21,018)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of unrealized net gain on equity securities	0						280	(280)
Balance at beginning of period at Dec. 31, 2017	991,457		938		29,953	503,709	481,331	(24,474)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	59,789						84,857	(25,068)
Cash dividends declared:
Preferred	(39)						(39)
Common	(12,767)						(12,767)
Conversion of Series D preferred stock		$ (938)		$ (938)
Purchase of shares of common stock	(97)								(97)
Issuance of shares of common stock	239,299				4,520	234,682			97
Stock based compensation	3,689					3,689
Balance at end of period at Sep. 30, 2018	$ 1,280,393		$ 0		$ 34,473	$ 742,080	$ 553,662	$ (49,822)	$ 0