Allowance for Loan Losses - Impaired Loans (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	$ 15,569	$ 48,095	$ 35,505
Unpaid principal, With no related allowance recorded	20,664	57,909	43,892
Average recorded Investment, With no related allowance recorded	25,536	48,279	41,984
Interest income Recognized, With no related allowance recorded	227	836	1,031
Recorded investment, With an allowance recorded	7,141	9,999	7,917
Unpaid principal, With an allowance recorded	7,393	10,938	8,249
Related allowance, With an allowance recorded	1,672	3,518	2,450
Average recorded Investment, With an allowance recorded	7,531	10,510	9,469
Interest income Recognized, With an allowance recorded	132	166	302
PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	3,789	4,626	3,056
Unpaid principal, With no related allowance recorded	4,258	4,813	3,277
Average recorded Investment, With no related allowance recorded	3,423	2,875	2,090
Interest income Recognized, With no related allowance recorded		78	87
Recorded investment, With an allowance recorded	1,428	2,306	3,627
Unpaid principal, With an allowance recorded	1,428	2,334	3,744
Related allowance, With an allowance recorded	498	727	440
Average recorded Investment, With an allowance recorded	2,527	1,972	2,631
Interest income Recognized, With an allowance recorded	29	31	174
Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	2,861	2,475	2,963
Unpaid principal, With no related allowance recorded	5,267	5,340	6,079
Average recorded Investment, With no related allowance recorded	2,912	2,738	2,982
Interest income Recognized, With no related allowance recorded	12	2	23
Recorded investment, With an allowance recorded	1,115	2,513	1,724
Unpaid principal, With an allowance recorded	1,166	2,973	1,904
Related allowance, With an allowance recorded	268	1,481	525
Average recorded Investment, With an allowance recorded	1,420	2,849	2,455
Interest income Recognized, With an allowance recorded	9	25	31
Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	512	637	454
Unpaid principal, With no related allowance recorded	578	696	505
Average recorded Investment, With no related allowance recorded	483	492	400
Interest income Recognized, With no related allowance recorded		1	3
Recorded investment, With an allowance recorded	496	511	606
Unpaid principal, With an allowance recorded	496	512	612
Related allowance, With an allowance recorded	238	298	80
Average recorded Investment, With an allowance recorded	551	474	521
Interest income Recognized, With an allowance recorded	11	9	14
Other Consumer [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	9	23	20
Unpaid principal, With no related allowance recorded	13	46	35
Average recorded Investment, With no related allowance recorded	13	31	29
Recorded investment, With an allowance recorded		37	1
Unpaid principal, With an allowance recorded		47	1
Related allowance, With an allowance recorded		15	1
Average recorded Investment, With an allowance recorded	1	41	23
Other Consumer [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	8	42	33
Unpaid principal, With no related allowance recorded	9	62	52
Average recorded Investment, With no related allowance recorded	21	40	35
Interest income Recognized, With no related allowance recorded			1
Recorded investment, With an allowance recorded	260	301	234
Unpaid principal, With an allowance recorded	260	301	234
Related allowance, With an allowance recorded	87	113	73
Average recorded Investment, With an allowance recorded	247	261	227
Interest income Recognized, With an allowance recorded	6	6	11
C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	321	338	576
Unpaid principal, With no related allowance recorded	356	366	688
Average recorded Investment, With no related allowance recorded	448	375	494
Interest income Recognized, With no related allowance recorded	8	11	29
Recorded investment, With an allowance recorded	1,609	1,706	2,094
Unpaid principal, With an allowance recorded	1,655	1,808	2,117
Related allowance, With an allowance recorded	647	676	1,187
Average recorded Investment, With an allowance recorded	1,852	1,522	1,716
Interest income Recognized, With an allowance recorded	36	42	122
C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded		4	1
Unpaid principal, With no related allowance recorded		4	1
Average recorded Investment, With no related allowance recorded	1	5	4
Home Equity Loans [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	1,217	779	947
Unpaid principal, With no related allowance recorded	1,871	1,256	1,349
Average recorded Investment, With no related allowance recorded	1,082	764	848
Interest income Recognized, With no related allowance recorded	8		5
Recorded investment, With an allowance recorded	657	598	674
Unpaid principal, With an allowance recorded	687	704	701
Related allowance, With an allowance recorded	203	346	256
Average recorded Investment, With an allowance recorded	666	551	589
Interest income Recognized, With an allowance recorded	12	3	26
Home Equity Loans [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	70	20	71
Unpaid principal, With no related allowance recorded	76	22	73
Average recorded Investment, With no related allowance recorded	70	22	48
Interest income Recognized, With no related allowance recorded			2
Recorded investment, With an allowance recorded		41	39
Unpaid principal, With an allowance recorded		42	40
Related allowance, With an allowance recorded		41	39
Average recorded Investment, With an allowance recorded	19	20	19
Auto Indirect [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Unpaid principal, With no related allowance recorded	7
Average recorded Investment, With no related allowance recorded	1
Construction [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	11	328	4
Unpaid principal, With no related allowance recorded	16	376	65
Average recorded Investment, With no related allowance recorded	8	1,364	1,202
Interest income Recognized, With no related allowance recorded		9
Average recorded Investment, With an allowance recorded		141	141
Construction [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded		88
Unpaid principal, With no related allowance recorded		183
Average recorded Investment, With no related allowance recorded		94	50
Construction [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded			490
Unpaid principal, With no related allowance recorded			490
Average recorded Investment, With no related allowance recorded	245		245
Interest income Recognized, With no related allowance recorded			18
RE Mortgage [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	3,223	3,770	3,886
Unpaid principal, With no related allowance recorded	4,706	5,901	5,998
Average recorded Investment, With no related allowance recorded	3,554	3,528	3,586
Interest income Recognized, With no related allowance recorded	43	19	81
Recorded investment, With an allowance recorded	2,338	2,780	2,006
Unpaid principal, With an allowance recorded	2,418	2,958	2,073
Related allowance, With an allowance recorded	389	784	335
Average recorded Investment, With an allowance recorded	2,172	2,752	2,365
Interest income Recognized, With an allowance recorded	36	40	49
RE Mortgage [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	532	290	875
Unpaid principal, With no related allowance recorded	701	316	908
Average recorded Investment, With no related allowance recorded	704	317	609
Interest income Recognized, With no related allowance recorded		3	31
Recorded investment, With an allowance recorded	536	627
Unpaid principal, With an allowance recorded	536	643
Related allowance, With an allowance recorded	85	72
Average recorded Investment, With an allowance recorded	268	731	417
Interest income Recognized, With an allowance recorded	9	4
RE Mortgage [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	7,927	40,294	27,109
Unpaid principal, With no related allowance recorded	8,428	44,441	29,678
Average recorded Investment, With no related allowance recorded	17,518	39,385	32,793
Interest income Recognized, With no related allowance recorded	156	795	893
Recorded investment, With an allowance recorded	1,422	2,365	1,418
Unpaid principal, With an allowance recorded	1,467	2,448	1,453
Related allowance, With an allowance recorded	165	216	146
Average recorded Investment, With an allowance recorded	1,420	2,654	2,180
Interest income Recognized, With an allowance recorded	39	56	74
RE Mortgage [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	2,667	3,633	1,132
Unpaid principal, With no related allowance recorded	2,894	3,713	1,248
Average recorded Investment, With no related allowance recorded	1,899	1,999	749
Interest income Recognized, With no related allowance recorded		74	32
Recorded investment, With an allowance recorded	136	826	2,748
Unpaid principal, With an allowance recorded	136	836	2,858
Related allowance, With an allowance recorded	88	203	248
Average recorded Investment, With an allowance recorded	1,442	486	1,447
Interest income Recognized, With an allowance recorded	$ 3	$ 12	$ 149