Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Corporate securities	Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss).	Total
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
Increase (Decrease) in Stockholders' Equity
Comprehensive income			18,264	3,327	21,591
Cash dividends declared on common stock per share			(9,646)		(9,646)
Stock options exercised	$ 22	285			307
Stock options exercised (in shares)	9,002
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	$ 28	(28)
Restricted stock awards (in shares)	11,273
Stock issued pursuant to restricted stock units.	$ 95	(95)
Stock issued pursuant to restricted stock units (in shares)	37,802
Common stock repurchased	$ (90)	(3,157)			(3,247)
Common stock repurchased (in shares)	(36,073)
Share-based compensation expense		1,698			1,698
Balance at Mar. 31, 2017	$ 73,077	1,132,173	379,534	(4,884)	$ 1,579,900
Balance (in shares) at Mar. 31, 2017	29,230,734				29,230,734
Balance (in shares) Preferred Stock at Mar. 31, 2017					0
Balance at Dec. 31, 2017	$ 91,899	1,807,601	419,847	(10,427)	$ 2,308,920
Balance (in shares) at Dec. 31, 2017	36,759,656				36,759,656
Balance (in shares) Preferred Stock at Dec. 31, 2017					0
Increase (Decrease) in Stockholders' Equity
Comprehensive income			42,326	(16,976)	$ 25,350
Cash dividends declared on common stock per share			(12,138)		(12,138)
AOCI reclassification to retained earnings from adoption of ASU 2018-02 | ASU 2018- 02			2,947	(2,947)
Stock options exercised	$ 5	61			66
Stock options exercised (in shares)	2,240
Restricted stock awards	$ 3	(3)
Restricted stock awards (in shares)	1,169
Stock issued pursuant to restricted stock units.	$ 96	(96)
Stock issued pursuant to restricted stock units (in shares)	38,365
Common stock repurchased	$ (45)	(1,567)			(1,612)
Common stock repurchased (in shares)	(17,992)
Share-based compensation expense		1,993			1,993
Balance at Mar. 31, 2018	$ 91,958	$ 1,807,989	$ 452,982	$ (30,350)	$ 2,322,579
Balance (in shares) at Mar. 31, 2018	36,783,438				36,783,438
Balance (in shares) Preferred Stock at Mar. 31, 2018					0