Loans and Allowance for Loan Losses - Table of loan payment estimates - (Details) - USD ($) $ in Thousands	Nov. 30, 2017	Jan. 03, 2017	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Acquired credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Contractual principal and interest			$ 721,606		$ 795,850	$ 774,471
Non-accretable difference			(43,397)		(39,324)	(28,966)
Cash flows expected to be collected			678,209		756,526	745,505
Accretable Yield			(121,804)		(133,096)	(139,283)
Carrying value			556,405		623,430	606,222
Allowance for loan losses on acquired loans			(4,426)	$ (4,084)	(4,627)	(3,741)	$ (4,556)	$ (3,395)
Acquired credit impaired loans | Park Sterling Corporation
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Contractual principal and interest	$ 113,584
Non-accretable difference	(27,248)
Cash flows expected to be collected	86,336
Accretable difference	(7,369)
Carrying value	78,967
Acquired credit impaired loans | Southeastern Bank Financial
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Contractual principal and interest		$ 78,963
Non-accretable difference		(13,072)
Cash flows expected to be collected		65,891
Accretable difference		(4,910)
Carrying value		60,981
Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			3,076,424		3,507,907	1,585,981
Acquired non-credit impaired loans accounted under FASB 310 20 | Park Sterling Corporation
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Contractual principal and interest	2,100,000
After fair value adjustment	2,200,000
Fair value adjustment	$ 46,500
Acquired credit impaired loans accounted under FASB 310 30
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			556,405		623,430	606,222
Allowance for loan losses on acquired loans			(4,426)		(4,627)	(3,741)
Impaired non-acquired and acquired loans accounted under FASB ASC topic 310-20 | Southeastern Bank Financial
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Contractual principal and interest		1,000,000
Carrying value		986,500
Fair value adjustment		$ 18,800
Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			3,076,424		3,507,907	1,585,981
Residential real estate | Acquired credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			229,502		260,787	256,602
Allowance for loan losses on acquired loans			(2,514)	(2,509)	(3,553)	(2,741)	(3,108)	(2,419)
Residential real estate | Acquired credit impaired loans accounted under FASB 310 30
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			229,502		260,787	256,602
Commercial non-owner occupied real estate | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			1,033,747		1,220,523	322,415
Commercial owner occupied real estate loan | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			486,254		521,818	221,566
Commercial owner occupied real estate loan | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			486,254		521,818	221,566
Consumer real estate | Acquired credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			45,633			56,362
Allowance for loan losses on acquired loans			(572)	(594)	(461)	(548)	(589)	(558)
Consumer real estate | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			955,502		1,031,202	697,235
Consumer real estate | Acquired credit impaired loans accounted under FASB 310 30
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			45,633		51,453	56,362
Consumer real estate | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			1,082,167		1,170,201	840,713
Commercial and industrial | Acquired credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			12,580		26,946	25,486
Allowance for loan losses on acquired loans			(128)	(505)	(145)	(320)	(394)	(238)
Commercial and industrial | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			304,864		398,696	117,884
Commercial and industrial | Acquired credit impaired loans accounted under FASB 310 30
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			12,580		26,946	25,486
Commercial and industrial | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			304,864		398,696	117,884
Other income producing property | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			169,392		196,669	83,403
Other income producing property | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			169,392		196,669	83,403
Consumer | Acquired credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			45,633		51,453	56,362
Consumer | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			126,665		137,710	143,478
Commercial | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			1,994,257		2,337,706	745,268
Other loans | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value					1,289
Other loans | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value					1,289
Construction and land development | Commercial non-owner occupied real estate | Acquired credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			40,951		49,649	52,977
Allowance for loan losses on acquired loans			(576)	(215)	(180)	(92)	(130)	(139)
Construction and land development | Commercial non-owner occupied real estate | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			281,282		403,357	112,855
Construction and land development | Commercial non-owner occupied real estate | Acquired credit impaired loans accounted under FASB 310 30
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			40,951		49,649	52,977
Construction and land development | Commercial non-owner occupied real estate | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			281,282		403,357	112,855
Other commercial non-owner occupied real estate | Commercial non-owner occupied real estate | Acquired credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			227,739		234,595	214,795
Allowance for loan losses on acquired loans			(636)	$ (261)	(288)	(40)	$ (335)	$ (41)
Other commercial non-owner occupied real estate | Commercial non-owner occupied real estate | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			752,465		817,166	209,560
Other commercial non-owner occupied real estate | Commercial non-owner occupied real estate | Acquired credit impaired loans accounted under FASB 310 30
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			227,739		234,595	214,795
Other commercial non-owner occupied real estate | Commercial non-owner occupied real estate | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			752,465		817,166	209,560
Home equity loans | Consumer real estate | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			278,906		320,591	177,129
Home equity loans | Consumer real estate | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			278,906		320,591	177,129
Consumer | Consumer real estate | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			126,665		137,710	143,478
Consumer Owner Occupied Loans | Consumer real estate | Acquired non-credit impaired loans accounted under FASB 310 20
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			676,596		710,611	520,106
Consumer Owner Occupied Loans | Consumer real estate | Acquired non-credit impaired loans
Contractual loan payments receivable, estimates of amounts not expected to be collected, other fair value adjustments and the resulting fair values of acquired loans
Carrying value			$ 676,596		$ 710,611	$ 520,106