Assets Acquired in FDIC-Assisted Acquisitions - Components of Covered Assets (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Covered Assets [Line Items]
Covered loans	$ 265,488	$ 414,855	$ 296,724
Less: Fair value adjustments	19,743	42,161	25,445
Total covered loans	245,745	372,694	271,279
OREO	18,531	52,092	23,408
Less: Fair value adjustments	2,442	9,456	3,501
Total covered OREO	16,089	42,636	19,907
Total covered assets	261,834	415,330	291,186
FDIC loss-share receivable (payable)	23,312	53,181	31,351	65,441
American United Bank (AUB) [Member]
Covered Assets [Line Items]
Covered loans		13,629
Less: Fair value adjustments		220
Total covered loans		13,409
OREO		4,264
Total covered OREO		4,264
Total covered assets		17,673
FDIC loss-share receivable (payable)	248	1,190	188
United Security Bank (USB) [Member]
Covered Assets [Line Items]
Covered loans	4,031	15,668	4,350
Less: Fair value adjustments	19	935	150
Total covered loans	4,012	14,733	4,200
OREO	165	3,366	165
Less: Fair value adjustments		135
Total covered OREO	165	3,231	165
Total covered assets	4,177	17,964	4,365
FDIC loss-share receivable (payable)	(1,216)	535	(1,197)
Satilla Community Bank (SCB) [Member]
Covered Assets [Line Items]
Covered loans	23,803	33,896	26,686
Less: Fair value adjustments	512	1,274	602
Total covered loans	23,291	32,622	26,084
OREO	2,474	3,122	2,849
Less: Fair value adjustments	389	303	389
Total covered OREO	2,085	2,819	2,460
Total covered assets	25,376	35,441	28,544
FDIC loss-share receivable (payable)	2,093	2,781	1,828
First Bank of Jacksonville (FBJ) [Member]
Covered Assets [Line Items]
Covered loans	19,409	24,281	21,243
Less: Fair value adjustments	1,539	2,768	1,825
Total covered loans	17,870	21,513	19,418
OREO	427	1,850	632
Less: Fair value adjustments	56	253
Total covered OREO	371	1,597	632
Total covered assets	18,241	23,110	20,050
FDIC loss-share receivable (payable)	1,366	3,034	1,885
Darby Bank & Trust (DBT) [Member]
Covered Assets [Line Items]
Covered loans	53,832	100,909	64,338
Less: Fair value adjustments	4,740	13,138	6,437
Total covered loans	49,092	87,771	57,901
OREO	5,716	12,250	6,655
Less: Fair value adjustments	381	1,092	514
Total covered OREO	5,335	11,158	6,141
Total covered assets	54,427	98,929	64,042
FDIC loss-share receivable (payable)	3,576	14,947	6,860
Tifton Banking Company (TBC) [Member]
Covered Assets [Line Items]
Covered loans	21,068	31,576	23,487
Less: Fair value adjustments	570	2,119	1,117
Total covered loans	20,498	29,457	22,370
OREO	1,698	4,681	2,388
Less: Fair value adjustments	162	761	367
Total covered OREO	1,536	3,920	2,021
Total covered assets	22,034	33,377	24,391
FDIC loss-share receivable (payable)	1,545	3,425	3,287
High Trust Bank (HTB) [Member]
Covered Assets [Line Items]
Covered loans	48,384	61,560	52,699
Less: Fair value adjustments	4,331	6,630	5,120
Total covered loans	44,053	54,930	47,579
OREO	2,885	7,263	3,670
Less: Fair value adjustments	938	2,349	1,283
Total covered OREO	1,947	4,914	2,387
Total covered assets	46,000	59,844	49,966
FDIC loss-share receivable (payable)	7,069	8,540	6,459
One Georgia Bank (OGB) [Member]
Covered Assets [Line Items]
Covered loans	38,699	55,569	42,971
Less: Fair value adjustments	2,409	4,653	3,785
Total covered loans	36,290	50,916	39,186
OREO	1,435	8,169	2,244
Less: Fair value adjustments	39	2,984	39
Total covered OREO	1,396	5,185	2,205
Total covered assets	37,686	56,101	41,391
FDIC loss-share receivable (payable)	2,748	6,815	3,906
Central Bank of Georgia (CBG) [Member]
Covered Assets [Line Items]
Covered loans	56,262	77,767	60,950
Less: Fair value adjustments	5,623	10,424	6,409
Total covered loans	50,639	67,343	54,541
OREO	3,731	7,127	4,805
Less: Fair value adjustments	477	1,579	909
Total covered OREO	3,254	5,548	3,896
Total covered assets	53,893	72,891	58,437
FDIC loss-share receivable (payable)	$ 5,883	$ 11,914	$ 8,135