Allowance for Loan Losses - Impaired Loans (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	$ 13,243	$ 49,253	$ 35,505
Unpaid principal, With no related allowance recorded	15,442	58,582	43,892
Average recorded Investment, With no related allowance recorded	24,372	48,859	41,984
Interest income Recognized, With no related allowance recorded	356	1,237	1,031
Recorded investment, With an allowance recorded	12,246	7,944	7,917
Unpaid principal, With an allowance recorded	12,467	8,276	8,249
Related allowance, With an allowance recorded	2,314	2,013	2,450
Average recorded Investment, With an allowance recorded	10,082	9,483	9,469
Interest income Recognized, With an allowance recorded	391	209	302
PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	2,953	2,547	3,056
Unpaid principal, With no related allowance recorded	3,223	2,795	3,277
Average recorded Investment, With no related allowance recorded	3,004	1,837	2,090
Interest income Recognized, With no related allowance recorded	10	35	87
Recorded investment, With an allowance recorded	1,161	3,730	3,627
Unpaid principal, With an allowance recorded	1,161	3,806	3,744
Related allowance, With an allowance recorded	507	521	440
Average recorded Investment, With an allowance recorded	2,394	2,684	2,631
Interest income Recognized, With an allowance recorded	36	82	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	1,888	2,966	2,963
Unpaid principal, With no related allowance recorded	2,318	6,142	6,079
Average recorded Investment, With no related allowance recorded	2,425	2,983	2,982
Interest income Recognized, With no related allowance recorded	26	16	23
Recorded investment, With an allowance recorded	923	2,229	1,724
Unpaid principal, With an allowance recorded	931	2,344	1,904
Related allowance, With an allowance recorded	263	858	525
Average recorded Investment, With an allowance recorded	1,324	2,707	2,455
Interest income Recognized, With an allowance recorded	16	36	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	502	411	454
Unpaid principal, With no related allowance recorded	573	451	505
Average recorded Investment, With no related allowance recorded	478	379	400
Interest income Recognized, With no related allowance recorded	2	1	3
Recorded investment, With an allowance recorded	507	606	606
Unpaid principal, With an allowance recorded	507	612	612
Related allowance, With an allowance recorded	248	80	80
Average recorded Investment, With an allowance recorded	557	521	521
Interest income Recognized, With an allowance recorded	16	11	14
Other Consumer [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	7	24	20
Unpaid principal, With no related allowance recorded	11	40	35
Average recorded Investment, With no related allowance recorded	12	31	29
Recorded investment, With an allowance recorded	8	4	1
Unpaid principal, With an allowance recorded	8	4	1
Related allowance, With an allowance recorded	3	4	1
Average recorded Investment, With an allowance recorded	4	24	23
Other Consumer [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	6	43	33
Unpaid principal, With no related allowance recorded	7	110	52
Average recorded Investment, With no related allowance recorded	19	40	35
Interest income Recognized, With no related allowance recorded		2	1
Recorded investment, With an allowance recorded	257	222	234
Unpaid principal, With an allowance recorded	257	222	234
Related allowance, With an allowance recorded	69	82	73
Average recorded Investment, With an allowance recorded	246	221	227
Interest income Recognized, With an allowance recorded	8	8	11
C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	574	380	576
Unpaid principal, With no related allowance recorded	749	413	688
Average recorded Investment, With no related allowance recorded	575	396	494
Interest income Recognized, With no related allowance recorded	26	16	29
Recorded investment, With an allowance recorded	1,823	1,201	2,094
Unpaid principal, With an allowance recorded	1,869	1,301	2,117
Related allowance, With an allowance recorded	822	441	1,187
Average recorded Investment, With an allowance recorded	1,959	1,270	1,716
Interest income Recognized, With an allowance recorded	55	48	122
C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded		3	1
Unpaid principal, With no related allowance recorded		3	1
Average recorded Investment, With no related allowance recorded	1	5	4
Recorded investment, With an allowance recorded		5
Unpaid principal, With an allowance recorded		5
Related allowance, With an allowance recorded		5
Average recorded Investment, With an allowance recorded		3
Home Equity Loans [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	1,239	1,075	947
Unpaid principal, With no related allowance recorded	1,763	1,488	1,349
Average recorded Investment, With no related allowance recorded	1,093	913	848
Interest income Recognized, With no related allowance recorded	8		5
Recorded investment, With an allowance recorded	775	274	674
Unpaid principal, With an allowance recorded	831	297	701
Related allowance, With an allowance recorded	152	169	256
Average recorded Investment, With an allowance recorded	725	389	589
Interest income Recognized, With an allowance recorded	21	4	26
Home Equity Loans [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	97	18	71
Unpaid principal, With no related allowance recorded	103	20	73
Average recorded Investment, With no related allowance recorded	84	22	48
Interest income Recognized, With no related allowance recorded	1		2
Recorded investment, With an allowance recorded		92	39
Unpaid principal, With an allowance recorded		93	40
Related allowance, With an allowance recorded		49	39
Average recorded Investment, With an allowance recorded	19	46	19
Interest income Recognized, With an allowance recorded		2
Auto Indirect [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
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	318	4
Unpaid principal, With no related allowance recorded	16	422	65
Average recorded Investment, With no related allowance recorded	7	1,359	1,202
Interest income Recognized, With no related allowance recorded		13
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		80
Unpaid principal, With no related allowance recorded		90
Average recorded Investment, With no related allowance recorded		90	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	2,376	4,281	3,886
Unpaid principal, With no related allowance recorded	3,060	6,637	5,998
Average recorded Investment, With no related allowance recorded	3,131	3,784	3,586
Interest income Recognized, With no related allowance recorded	63	43	81
Recorded investment, With an allowance recorded	2,302	2,019	2,006
Unpaid principal, With an allowance recorded	2,390	2,082	2,073
Related allowance, With an allowance recorded	342	345	335
Average recorded Investment, With an allowance recorded	2,154	2,372	2,365
Interest income Recognized, With an allowance recorded	54	37	49
RE Mortgage [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	474	986	875
Unpaid principal, With no related allowance recorded	492	1,031	908
Average recorded Investment, With no related allowance recorded	674	665	609
Interest income Recognized, With no related allowance recorded	7	11	31
Recorded investment, With an allowance recorded	263
Unpaid principal, With an allowance recorded	263
Related allowance, With an allowance recorded	81
Average recorded Investment, With an allowance recorded	131	417	417
Interest income Recognized, With an allowance recorded	7
RE Mortgage [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	7,148	40,129	27,109
Unpaid principal, With no related allowance recorded	7,525	43,350	29,678
Average recorded Investment, With no related allowance recorded	17,128	39,303	32,793
Interest income Recognized, With no related allowance recorded	233	1,149	893
Recorded investment, With an allowance recorded	6,415	2,217	1,418
Unpaid principal, With an allowance recorded	6,438	2,248	1,453
Related allowance, With an allowance recorded	732	196	146
Average recorded Investment, With an allowance recorded	3,916	2,580	2,180
Interest income Recognized, With an allowance recorded	245	84	74
RE Mortgage [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	1,874	1,086	1,132
Unpaid principal, With no related allowance recorded	2,048	1,180	1,248
Average recorded Investment, With no related allowance recorded	1,503	726	749
Interest income Recognized, With no related allowance recorded		21	32
Recorded investment, With an allowance recorded	134	2,805	2,748
Unpaid principal, With an allowance recorded	134	2,874	2,858
Related allowance, With an allowance recorded	109	305	248
Average recorded Investment, With an allowance recorded	1,441	1,476	1,447
Interest income Recognized, With an allowance recorded	$ 5	$ 61	$ 149