Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Common Stock	Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss).	Total
Balance at Dec. 31, 2015	$ 60,407	$ 703,929	$ 298,919	$ (3,871)	$ 1,059,384
Balance (in shares) at Dec. 31, 2015	24,162,657
Increase (Decrease) in Stockholders' Equity
Comprehensive income			77,105	7,866	84,971
Cash dividends declared on common stock per share			(21,534)		(21,534)
Employee stock purchases	$ 19	455			474
Employee stock purchases (in shares)	7,793
Stock options exercised	$ 111	1,402			1,513
Stock options exercised (in shares)	44,491
Restricted stock awards	$ 99	(99)
Restricted stock awards (in shares)	39,431
Stock issued pursuant to restricted stock units.	$ 90	(90)
Stock issued pursuant to restricted stock units (in shares)	35,903
Value of common stock repurchased buyback plan	$ (82)	(2,048)			(2,130)
Common stock repurchased buyback plan (in shares)	(32,900)
Common stock repurchased	$ (121)	(3,129)			(3,250)
Common stock repurchased (in shares)	(48,253)
Share-based compensation expense		4,704			4,704
Balance at Sep. 30, 2016	$ 60,523	705,124	354,490	3,995	$ 1,124,132
Balance (in shares) at Sep. 30, 2016	24,209,122				24,209,122
Balance (in shares) Preferred Stock at Sep. 30, 2016					0
Balance at Dec. 31, 2016	$ 60,576	711,307	370,916	(8,211)	$ 1,134,588
Balance (in shares) at Dec. 31, 2016	24,230,392				24,230,392
Balance (in shares) Preferred Stock at Dec. 31, 2016					0
Increase (Decrease) in Stockholders' Equity
Comprehensive income			85,133	4,423	$ 89,556
Cash dividends declared on common stock per share			(28,956)		(28,956)
Employee stock purchases	$ 17	536			553
Employee stock purchases (in shares)	6,742
Stock options exercised	$ 84	1,050			1,134
Stock options exercised (in shares)	33,896
Common stock issued for Southeastern Bank Financial Corp. acquisition	$ 12,446	422,163			434,609
Common stock issued for Southeastern Bank Financial Corp. acquisition (in shares)	4,978,338
Restricted stock awards	$ 51	(51)
Restricted stock awards (in shares)	20,683
Stock issued pursuant to restricted stock units.	$ 95	(95)
Stock issued pursuant to restricted stock units (in shares)	37,802
Common stock repurchased	$ (101)	(3,525)			(3,626)
Common stock repurchased (in shares)	(40,484)
Share-based compensation expense		4,967			4,967
Balance at Sep. 30, 2017	$ 73,168	$ 1,136,352	$ 427,093	$ (3,788)	$ 1,632,825
Balance (in shares) at Sep. 30, 2017	29,267,369				29,267,369
Balance (in shares) Preferred Stock at Sep. 30, 2017					0