Assets Acquired in FDIC-Assisted Acquisitions - Components of Covered Assets (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Covered Assets [Line Items]
Covered loans	$ 226,440	$ 367,735	$ 296,724
Less: Fair value adjustments	16,842	36,485	25,445
Total covered loans	209,598	331,250	271,279
OREO	14,857	46,468	23,408
Less: Fair value adjustments	2,231	8,042	3,501
Total covered OREO	12,626	38,426	19,907
Total covered assets	222,224	369,676	291,186
FDIC indemnification asset	14,957	49,180	31,351	$ 65,441
American United Bank (AUB) [Member]
Covered Assets [Line Items]
Covered loans		9,106
Less: Fair value adjustments		133
Total covered loans		8,973
OREO		1,690
Total covered OREO		1,690
Total covered assets		10,663
FDIC indemnification asset	187	1,676	188
United Security Bank (USB) [Member]
Covered Assets [Line Items]
Covered loans	3,883	14,030	4,350
Less: Fair value adjustments	18	805	150
Total covered loans	3,865	13,225	4,200
OREO	165	2,927	165
Less: Fair value adjustments		62
Total covered OREO	165	2,865	165
Total covered assets	4,030	16,090	4,365
FDIC indemnification asset	(1,232)	920	(1,197)
Satilla Community Bank (SCB) [Member]
Covered Assets [Line Items]
Covered loans	5,318	30,545	26,686
Less: Fair value adjustments	209	954	602
Total covered loans	5,109	29,591	26,084
OREO	95	3,332	2,849
Less: Fair value adjustments		308	389
Total covered OREO	95	3,024	2,460
Total covered assets	5,204	32,615	28,544
FDIC indemnification asset	1,300	3,073	1,828
First Bank of Jacksonville (FBJ) [Member]
Covered Assets [Line Items]
Covered loans	17,708	23,264	21,243
Less: Fair value adjustments	1,286	2,696	1,825
Total covered loans	16,422	20,568	19,418
OREO	815	1,734	632
Less: Fair value adjustments	121	135
Total covered OREO	694	1,599	632
Total covered assets	17,116	22,167	20,050
FDIC indemnification asset	1,227	2,752	1,885
Darby Bank & Trust (DBT) [Member]
Covered Assets [Line Items]
Covered loans	46,269	81,700	64,338
Less: Fair value adjustments	3,667	8,774	6,437
Total covered loans	42,602	72,926	57,901
OREO	5,216	12,766	6,655
Less: Fair value adjustments	700	913	514
Total covered OREO	4,516	11,853	6,141
Total covered assets	47,118	84,779	64,042
FDIC indemnification asset	2,126	10,119	6,860
Tifton Banking Company (TBC) [Member]
Covered Assets [Line Items]
Covered loans	19,609	28,363	23,487
Less: Fair value adjustments	515	1,853	1,117
Total covered loans	19,094	26,510	22,370
OREO	1,480	4,493	2,388
Less: Fair value adjustments	116	758	367
Total covered OREO	1,364	3,735	2,021
Total covered assets	20,458	30,245	24,391
FDIC indemnification asset	521	3,543	3,287
High Trust Bank (HTB) [Member]
Covered Assets [Line Items]
Covered loans	47,176	59,267	52,699
Less: Fair value adjustments	4,127	6,535	5,120
Total covered loans	43,049	52,732	47,579
OREO	3,085	4,130	3,670
Less: Fair value adjustments	955	1,349	1,283
Total covered OREO	2,130	2,781	2,387
Total covered assets	45,179	55,513	49,966
FDIC indemnification asset	4,806	9,000	6,459
One Georgia Bank (OGB) [Member]
Covered Assets [Line Items]
Covered loans	34,218	49,501	42,971
Less: Fair value adjustments	2,192	4,937	3,785
Total covered loans	32,026	44,564	39,186
OREO	442	7,964	2,244
Less: Fair value adjustments		2,984	39
Total covered OREO	442	4,980	2,205
Total covered assets	32,468	49,544	41,391
FDIC indemnification asset	1,856	7,268	3,906
Central Bank of Georgia (CBG) [Member]
Covered Assets [Line Items]
Covered loans	52,259	71,959	60,950
Less: Fair value adjustments	4,828	9,798	6,409
Total covered loans	47,431	62,161	54,541
OREO	3,559	7,432	4,805
Less: Fair value adjustments	339	1,533	909
Total covered OREO	3,220	5,899	3,896
Total covered assets	50,651	68,060	58,437
FDIC indemnification asset	$ 4,166	$ 10,829	$ 8,135