Assets Acquired in FDIC-Assisted Acquisitions - Components of Covered Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Covered Assets [Line Items]
Covered loans	$ 296,724	$ 443,322
Less: Credit risk adjustments	25,445	53,085
Total covered loans	271,279	390,237
OREO	23,408	55,827
Less: Fair value adjustments	3,501	9,934
Total covered OREO	19,907	45,893
Total covered assets	291,186	436,130
FDIC loss-share receivable	31,351	65,441	159,724
American United Bank (AUB) [Member]
Covered Assets [Line Items]
Covered loans		15,787
Less: Credit risk adjustments		231
Total covered loans		15,556
OREO		4,264
Total covered OREO		4,264
Total covered assets		19,820
FDIC loss-share receivable	188	1,452
United Security Bank (USB) [Member]
Covered Assets [Line Items]
Covered loans	4,350	18,504
Less: Credit risk adjustments	150	1,427
Total covered loans	4,200	17,077
OREO	165	2,865
Less: Fair value adjustments		141
Total covered OREO	165	2,724
Total covered assets	4,365	19,801
FDIC loss-share receivable	(1,197)	889
Satilla Community Bank (SCB) [Member]
Covered Assets [Line Items]
Covered loans	26,686	34,637
Less: Credit risk adjustments	602	1,483
Total covered loans	26,084	33,154
OREO	2,849	3,461
Less: Fair value adjustments	389	303
Total covered OREO	2,460	3,158
Total covered assets	28,544	36,312
FDIC loss-share receivable	1,828	3,175
First Bank of Jacksonville (FBJ) [Member]
Covered Assets [Line Items]
Covered loans	21,243	25,891
Less: Credit risk adjustments	1,825	3,730
Total covered loans	19,418	22,161
OREO	632	1,880
Less: Fair value adjustments	0	242
Total covered OREO	632	1,638
Total covered assets	20,050	23,799
FDIC loss-share receivable	1,885	3,689
Darby Bank & Trust (DBT) [Member]
Covered Assets [Line Items]
Covered loans	64,338	105,157
Less: Credit risk adjustments	6,437	17,819
Total covered loans	57,901	87,338
OREO	6,655	17,023
Less: Fair value adjustments	514	1,282
Total covered OREO	6,141	15,741
Total covered assets	64,042	103,079
FDIC loss-share receivable	6,860	18,724
Tifton Banking Company (TBC) [Member]
Covered Assets [Line Items]
Covered loans	23,487	32,590
Less: Credit risk adjustments	1,117	2,354
Total covered loans	22,370	30,236
OREO	2,388	4,844
Less: Fair value adjustments	367	745
Total covered OREO	2,021	4,099
Total covered assets	24,391	34,335
FDIC loss-share receivable	3,287	3,721
High Trust Bank (HTB) [Member]
Covered Assets [Line Items]
Covered loans	52,699	67,126
Less: Credit risk adjustments	5,120	7,359
Total covered loans	47,579	59,767
OREO	3,670	6,374
Less: Fair value adjustments	1,283	2,304
Total covered OREO	2,387	4,070
Total covered assets	49,966	63,837
FDIC loss-share receivable	6,459	9,325
One Georgia Bank (OGB) [Member]
Covered Assets [Line Items]
Covered loans	42,971	58,512
Less: Credit risk adjustments	3,785	5,067
Total covered loans	39,186	53,445
OREO	2,244	7,506
Less: Fair value adjustments	39	2,984
Total covered OREO	2,205	4,522
Total covered assets	41,391	57,967
FDIC loss-share receivable	3,906	9,645
Central Bank of Georgia (CBG) [Member]
Covered Assets [Line Items]
Covered loans	60,950	85,118
Less: Credit risk adjustments	6,409	13,615
Total covered loans	54,541	71,503
OREO	4,805	7,610
Less: Fair value adjustments	909	1,933
Total covered OREO	3,896	5,677
Total covered assets	58,437	77,180
FDIC loss-share receivable	$ 8,135	$ 14,821