Loans and Allowance for Loan Losses - Summary of Impaired Loans Disaggregated by Class (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	$ 15,611	$ 14,958
Recorded Investment, With a related allowance recorded	17,487	20,776
Recorded Investment, Total	33,098	35,734
Unpaid Principal Balance, With no related allowance recorded	23,026	20,589
Unpaid Principal Balance, With a related allowance recorded	21,448	23,356
Unpaid Principal Balance, Total	44,474	43,945
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	1,318	768
Related Allowance, Total	1,318	768
Average Recorded Investment, With no related allowance recorded	13,768	23,083
Average Recorded Investment, With a related allowance recorded	25,845	38,833
Average Recorded Investment, Total	39,613	61,916
Interest Income Recognized, With no related allowance recorded	390	534
Interest Income Recognized, With a related allowance recorded	504	703
Interest Income Recognized, Total	894	1,237
Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	1,498	2,470
Recorded Investment, With a related allowance recorded	5,015	4,965
Recorded Investment, Total	6,513	7,435
Unpaid Principal Balance, With no related allowance recorded	3,841	3,717
Unpaid Principal Balance, With a related allowance recorded	5,243	5,303
Unpaid Principal Balance, Total	9,084	9,020
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	116	477
Related Allowance, Total	116	477
Average Recorded Investment, With no related allowance recorded	1,514	1,100
Average Recorded Investment, With a related allowance recorded	7,226	11,683
Average Recorded Investment, Total	8,740	12,783
Interest Income Recognized, With no related allowance recorded	31	26
Interest Income Recognized, With a related allowance recorded	195	243
Interest Income Recognized, Total	226	269
Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	3,320	4,829
Recorded Investment, With a related allowance recorded	5,581	6,498
Recorded Investment, Total	8,901	11,327
Unpaid Principal Balance, With no related allowance recorded	5,459	6,273
Unpaid Principal Balance, With a related allowance recorded	8,650	8,343
Unpaid Principal Balance, Total	14,109	14,616
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	676	22
Related Allowance, Total	676	22
Average Recorded Investment, With no related allowance recorded	3,339	3,076
Average Recorded Investment, With a related allowance recorded	7,708	2,706
Average Recorded Investment, Total	11,047	5,782
Interest Income Recognized, With no related allowance recorded	112	85
Interest Income Recognized, With a related allowance recorded	145
Interest Income Recognized, Total	257	85
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	10,502	7,186
Recorded Investment, With a related allowance recorded	4,442	8,708
Recorded Investment, Total	14,944	15,894
Unpaid Principal Balance, With no related allowance recorded	13,011	10,092
Unpaid Principal Balance, With a related allowance recorded	4,797	9,090
Unpaid Principal Balance, Total	17,808	19,182
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	144	268
Related Allowance, Total	144	268
Average Recorded Investment, With no related allowance recorded	8,739	17,225
Average Recorded Investment, With a related allowance recorded	8,722	22,346
Average Recorded Investment, Total	17,461	39,571
Interest Income Recognized, With no related allowance recorded	246	423
Interest Income Recognized, With a related allowance recorded	136	460
Interest Income Recognized, Total	382	883
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	291	473
Recorded Investment, With a related allowance recorded	2,449	605
Recorded Investment, Total	2,740	1,078
Unpaid Principal Balance, With no related allowance recorded	715	507
Unpaid Principal Balance, With a related allowance recorded	2,758	620
Unpaid Principal Balance, Total	3,473	1,127
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	382	1
Related Allowance, Total	382	1
Average Recorded Investment, With no related allowance recorded	176	669
Average Recorded Investment, With a related allowance recorded	2,189	1,073
Average Recorded Investment, Total	2,365	1,742
Interest Income Recognized, With no related allowance recorded	1
Interest Income Recognized, With a related allowance recorded	28
Interest Income Recognized, Total	29
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded		1,013
Average Recorded Investment, With a related allowance recorded		1,025
Average Recorded Investment, Total		2,038
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	15,583	9,751
Recorded Investment, With a related allowance recorded	13,814	20,776
Recorded Investment, Total	29,397	30,527
Unpaid Principal Balance, With no related allowance recorded	21,228	13,031
Unpaid Principal Balance, With a related allowance recorded	15,050	23,356
Unpaid Principal Balance, Total	36,278	36,387
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	754	768
Related Allowance, Total	754	768
Average Recorded Investment, With no related allowance recorded	12,891	20,176
Average Recorded Investment, With a related allowance recorded	22,106	32,421
Average Recorded Investment, Total	34,997	52,597
Interest Income Recognized, With no related allowance recorded	390	474
Interest Income Recognized, With a related allowance recorded	280	640
Interest Income Recognized, Total	670	1,114
Originated Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	1,498	329
Recorded Investment, With a related allowance recorded	4,084	4,965
Recorded Investment, Total	5,582	5,294
Unpaid Principal Balance, With no related allowance recorded	2,111	442
Unpaid Principal Balance, With a related allowance recorded	4,173	5,303
Unpaid Principal Balance, Total	6,284	5,745
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	24	477
Related Allowance, Total	24	477
Average Recorded Investment, With no related allowance recorded	1,157	235
Average Recorded Investment, With a related allowance recorded	5,922	8,936
Average Recorded Investment, Total	7,079	9,171
Interest Income Recognized, With no related allowance recorded	31	18
Interest Income Recognized, With a related allowance recorded	77	180
Interest Income Recognized, Total	108	198
Originated Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	3,320	4,101
Recorded Investment, With a related allowance recorded	3,297	6,498
Recorded Investment, Total	6,617	10,599
Unpaid Principal Balance, With no related allowance recorded	5,459	5,131
Unpaid Principal Balance, With a related allowance recorded	3,815	8,343
Unpaid Principal Balance, Total	9,274	13,474
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	250	22
Related Allowance, Total	250	22
Average Recorded Investment, With no related allowance recorded	3,218	2,780
Average Recorded Investment, With a related allowance recorded	6,578	2,549
Average Recorded Investment, Total	9,796	5,329
Interest Income Recognized, With no related allowance recorded	112	82
Interest Income Recognized, With a related allowance recorded	100
Interest Income Recognized, Total	212	82
Originated Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	10,502	5,321
Recorded Investment, With a related allowance recorded	3,984	8,708
Recorded Investment, Total	14,486	14,029
Unpaid Principal Balance, With no related allowance recorded	13,011	7,458
Unpaid Principal Balance, With a related allowance recorded	4,304	9,090
Unpaid Principal Balance, Total	17,315	16,548
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	98	268
Related Allowance, Total	98	268
Average Recorded Investment, With no related allowance recorded	8,428	15,886
Average Recorded Investment, With a related allowance recorded	7,417	19,683
Average Recorded Investment, Total	15,845	35,569
Interest Income Recognized, With no related allowance recorded	246	374
Interest Income Recognized, With a related allowance recorded	75	460
Interest Income Recognized, Total	321	834
Originated Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	263
Recorded Investment, With a related allowance recorded	2,449	605
Recorded Investment, Total	2,712	605
Unpaid Principal Balance, With no related allowance recorded	647
Unpaid Principal Balance, With a related allowance recorded	2,758	620
Unpaid Principal Balance, Total	3,405	620
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	382	1
Related Allowance, Total	382	1
Average Recorded Investment, With no related allowance recorded	88	262
Average Recorded Investment, With a related allowance recorded	2,189	228
Average Recorded Investment, Total	2,277	490
Interest Income Recognized, With no related allowance recorded	1
Interest Income Recognized, With a related allowance recorded	28
Interest Income Recognized, Total	29
Originated Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded		1,013
Average Recorded Investment, With a related allowance recorded		1,025
Average Recorded Investment, Total		2,038
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	28	5,207
Recorded Investment, With a related allowance recorded	3,673
Recorded Investment, Total	3,701	5,207
Unpaid Principal Balance, With no related allowance recorded	1,798	7,558
Unpaid Principal Balance, With a related allowance recorded	6,398
Unpaid Principal Balance, Total	8,196	7,558
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	564
Related Allowance, Total	564
Average Recorded Investment, With no related allowance recorded	877	2,907
Average Recorded Investment, With a related allowance recorded	3,739	6,412
Average Recorded Investment, Total	4,616	9,319
Interest Income Recognized, With no related allowance recorded		60
Interest Income Recognized, With a related allowance recorded	224	63
Interest Income Recognized, Total	224	123
Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded		2,141
Recorded Investment, With a related allowance recorded	931
Recorded Investment, Total	931	2,141
Unpaid Principal Balance, With no related allowance recorded	1,730	3,275
Unpaid Principal Balance, With a related allowance recorded	1,070
Unpaid Principal Balance, Total	2,800	3,275
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	92
Related Allowance, Total	92
Average Recorded Investment, With no related allowance recorded	357	865
Average Recorded Investment, With a related allowance recorded	1,304	2,747
Average Recorded Investment, Total	1,661	3,612
Interest Income Recognized, With no related allowance recorded		8
Interest Income Recognized, With a related allowance recorded	118	63
Interest Income Recognized, Total	118	71
Acquired Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded		728
Recorded Investment, With a related allowance recorded	2,284
Recorded Investment, Total	2,284	728
Unpaid Principal Balance, With no related allowance recorded		1,142
Unpaid Principal Balance, With a related allowance recorded	4,835
Unpaid Principal Balance, Total	4,835	1,142
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	426
Related Allowance, Total	426
Average Recorded Investment, With no related allowance recorded	121	296
Average Recorded Investment, With a related allowance recorded	1,130	157
Average Recorded Investment, Total	1,251	453
Interest Income Recognized, With no related allowance recorded		3
Interest Income Recognized, With a related allowance recorded	45
Interest Income Recognized, Total	45	3
Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded		1,865
Recorded Investment, With a related allowance recorded	458
Recorded Investment, Total	458	1,865
Unpaid Principal Balance, With no related allowance recorded		2,634
Unpaid Principal Balance, With a related allowance recorded	493
Unpaid Principal Balance, Total	493	2,634
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded	46
Related Allowance, Total	46
Average Recorded Investment, With no related allowance recorded	311	1,339
Average Recorded Investment, With a related allowance recorded	1,305	2,663
Average Recorded Investment, Total	1,616	4,002
Interest Income Recognized, With no related allowance recorded		49
Interest Income Recognized, With a related allowance recorded	61
Interest Income Recognized, Total	61	49
Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	28	473
Recorded Investment, With a related allowance recorded
Recorded Investment, Total	28	473
Unpaid Principal Balance, With no related allowance recorded	68	507
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total	68	507
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded	88	407
Average Recorded Investment, With a related allowance recorded		845
Average Recorded Investment, Total	88	1,252
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded
Average Recorded Investment, With a related allowance recorded
Average Recorded Investment, Total
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded
Average Recorded Investment, With a related allowance recorded
Average Recorded Investment, Total
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Covered Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded
Average Recorded Investment, With a related allowance recorded
Average Recorded Investment, Total
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Covered Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded
Average Recorded Investment, With a related allowance recorded
Average Recorded Investment, Total
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Covered Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded
Average Recorded Investment, With a related allowance recorded
Average Recorded Investment, Total
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Covered Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded
Average Recorded Investment, With a related allowance recorded
Average Recorded Investment, Total
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total
Covered Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded
Recorded Investment, With a related allowance recorded
Recorded Investment, Total
Unpaid Principal Balance, With no related allowance recorded
Unpaid Principal Balance, With a related allowance recorded
Unpaid Principal Balance, Total
Related Allowance, With no related allowance recorded
Related Allowance, With a related allowance recorded
Related Allowance, Total
Average Recorded Investment, With no related allowance recorded
Average Recorded Investment, With a related allowance recorded
Average Recorded Investment, Total
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With a related allowance recorded
Interest Income Recognized, Total