Loans and Allowance for Loan Losses - Table of loan payment estimates - (Details) - USD ($) $ in Thousands	Nov. 30, 2017	Jan. 03, 2017	Mar. 31, 2018	Dec. 31, 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			$ 765,057	$ 795,850	$ 812,892
Non-accretable difference			(33,841)	(39,324)	(31,273)
Cash flows expected to be collected			731,216	756,526	781,619
Accretable Yield			(129,858)	(133,096)	(149,723)
Carrying value			601,358	623,430	631,896
Allowance for loan losses on acquired loans			(4,084)	(4,627)	(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	$ 92,600
Non-accretable difference	(12,840)
Cash flows expected to be collected	79,760
Accretable difference	(8,829)
Carrying value	70,931
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		$ 73,365
Non-accretable difference		(12,912)
Cash flows expected to be collected		60,453
Accretable difference		(4,603)
Carrying value		55,850
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			3,274,938	3,507,907	1,715,642
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	2,200,000
After fair value adjustment	2,300,000
Fair value adjustment	$ 50,100
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			601,358	623,430	631,896
Allowance for loan losses on acquired loans			(4,084)	(4,627)	(4,556)
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		1,010,000
Carrying value		991,500
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			3,274,938	3,507,907	1,715,642
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			248,766	260,787	266,484
Allowance for loan losses on acquired loans			(2,509)	(3,553)	(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			248,766	260,787	266,484
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			1,132,998	1,220,523	359,747
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			498,541	521,818	238,612
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			498,541	521,818	238,612
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			48,801		58,688
Allowance for loan losses on acquired loans			(594)	(461)	(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			979,335	1,031,202	736,989
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			48,801	51,453	58,688
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			1,113,137	1,170,201	888,930
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			24,295	26,946	26,225
Allowance for loan losses on acquired loans			(505)	(145)	(395)	(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			344,171	398,696	136,309
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			24,295	26,946	26,225
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			344,171	398,696	136,309
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			186,091	196,669	92,044
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			186,091	196,669	92,044
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			48,801	51,453	58,688
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			133,802	137,710	151,941
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			2,161,801	2,337,706	826,712
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			46,219	49,649	57,343
Allowance for loan losses on acquired loans			(215)	(180)	(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			349,532	403,357	141,897
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			46,219	49,649	57,343
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			349,532	403,357	141,897
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			233,277	234,595	223,156
Allowance for loan losses on acquired loans			(261)	(288)	(334)	$ (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			783,466	817,166	217,850
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			233,277	234,595	223,156
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			783,466	817,166	217,850
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			295,721	320,591	186,411
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			295,721	320,591	186,411
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			133,802	137,710	151,941
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			683,614	710,611	550,578
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			$ 683,614	$ 710,611	$ 550,578