Allowance for Loan Losses - Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	$ 17,701	$ 35,505
Unpaid principal, With no related allowance recorded	18,641	43,892
Average recorded Investment, With no related allowance recorded	26,601	41,984
Interest income Recognized, With no related allowance recorded	757	1,031
Recorded investment, With an allowance recorded	6,285	7,917
Unpaid principal, With an allowance recorded	6,349	8,249
Related allowance, With an allowance recorded	1,544	2,450
Average recorded Investment, With an allowance recorded	7,100	9,469
Interest income Recognized, With an allowance recorded	206	302
PNCI Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	3,094	3,056
Unpaid principal, With no related allowance recorded	3,341	3,277
Average recorded Investment, With no related allowance recorded	3,075	2,090
Interest income Recognized, With no related allowance recorded	17	87
Recorded investment, With an allowance recorded	1,060	3,627
Unpaid principal, With an allowance recorded	1,060	3,744
Related allowance, With an allowance recorded	502	440
Average recorded Investment, With an allowance recorded	2,344	2,631
Interest income Recognized, With an allowance recorded	49	174
Mortgage Loans on Real Estate [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	1,691	3,886
Unpaid principal, With no related allowance recorded	1,699	5,998
Average recorded Investment, With no related allowance recorded	2,788	3,586
Interest income Recognized, With no related allowance recorded	83	81
Recorded investment, With an allowance recorded	1,372	2,006
Unpaid principal, With an allowance recorded	1,372	2,073
Related allowance, With an allowance recorded	170	335
Average recorded Investment, With an allowance recorded	1,689	2,365
Interest income Recognized, With an allowance recorded	56	49
Mortgage Loans on Real Estate [Member] | Residential [Member] | PNCI Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	463	875
Unpaid principal, With no related allowance recorded	486	908
Average recorded Investment, With no related allowance recorded	669	609
Interest income Recognized, With no related allowance recorded	7	31
Recorded investment, With an allowance recorded	259
Unpaid principal, With an allowance recorded	259
Related allowance, With an allowance recorded	79
Average recorded Investment, With an allowance recorded	130	417
Interest income Recognized, With an allowance recorded	10
Mortgage Loans on Real Estate [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	13,144	27,109
Unpaid principal, With no related allowance recorded	13,488	29,678
Average recorded Investment, With no related allowance recorded	20,126	32,793
Interest income Recognized, With no related allowance recorded	581	893
Recorded investment, With an allowance recorded	646	1,418
Unpaid principal, With an allowance recorded	646	1,453
Related allowance, With an allowance recorded	19	146
Average recorded Investment, With an allowance recorded	1,032	2,180
Interest income Recognized, With an allowance recorded	37	74
Mortgage Loans on Real Estate [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	1,826	1,132
Unpaid principal, With no related allowance recorded	2,031	1,248
Average recorded Investment, With no related allowance recorded	1,479	749
Interest income Recognized, With no related allowance recorded		32
Recorded investment, With an allowance recorded	132	2,748
Unpaid principal, With an allowance recorded	132	2,858
Related allowance, With an allowance recorded	108	248
Average recorded Investment, With an allowance recorded	1,440	1,447
Interest income Recognized, With an allowance recorded	7	149
Consumer [Member] | Home Equity Lines of Credit [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	1,480	2,963
Unpaid principal, With no related allowance recorded	1,561	6,079
Average recorded Investment, With no related allowance recorded	2,221	2,982
Interest income Recognized, With no related allowance recorded	40	23
Recorded investment, With an allowance recorded	430	1,724
Unpaid principal, With an allowance recorded	440	1,904
Related allowance, With an allowance recorded	110	525
Average recorded Investment, With an allowance recorded	1,077	2,455
Interest income Recognized, With an allowance recorded	9	31
Consumer [Member] | Home Equity Lines of Credit [Member] | PNCI Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	735	454
Unpaid principal, With no related allowance recorded	746	505
Average recorded Investment, With no related allowance recorded	594	400
Interest income Recognized, With no related allowance recorded	9	3
Recorded investment, With an allowance recorded	551	606
Unpaid principal, With an allowance recorded	551	612
Related allowance, With an allowance recorded	300	80
Average recorded Investment, With an allowance recorded	579	521
Interest income Recognized, With an allowance recorded	27	14
Consumer [Member] | Home Equity Loans [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	598	947
Unpaid principal, With no related allowance recorded	922	1,349
Average recorded Investment, With no related allowance recorded	773	848
Interest income Recognized, With no related allowance recorded	4	5
Recorded investment, With an allowance recorded	485	674
Unpaid principal, With an allowance recorded	487	701
Related allowance, With an allowance recorded	102	256
Average recorded Investment, With an allowance recorded	579	589
Interest income Recognized, With an allowance recorded	25	26
Consumer [Member] | Home Equity Loans [Member] | PNCI Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	67	71
Unpaid principal, With no related allowance recorded	74	73
Average recorded Investment, With no related allowance recorded	69	48
Interest income Recognized, With no related allowance recorded	1	2
Recorded investment, With an allowance recorded		39
Unpaid principal, With an allowance recorded		40
Related allowance, With an allowance recorded		39
Average recorded Investment, With an allowance recorded	19	19
Consumer [Member] | Auto Indirect [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded Investment, With no related allowance recorded	1
Consumer [Member] | Other Consumer [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	15	20
Unpaid principal, With no related allowance recorded	29	35
Average recorded Investment, With no related allowance recorded	16	29
Interest income Recognized, With no related allowance recorded	1
Recorded investment, With an allowance recorded	18	1
Unpaid principal, With an allowance recorded	19	1
Related allowance, With an allowance recorded	13	1
Average recorded Investment, With an allowance recorded	9	23
Interest income Recognized, With an allowance recorded	2
Consumer [Member] | Other Consumer [Member] | PNCI Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	3	33
Unpaid principal, With no related allowance recorded	4	52
Average recorded Investment, With no related allowance recorded	18	35
Interest income Recognized, With no related allowance recorded		1
Recorded investment, With an allowance recorded	118	234
Unpaid principal, With an allowance recorded	118	234
Related allowance, With an allowance recorded	15	73
Average recorded Investment, With an allowance recorded	176	227
Interest income Recognized, With an allowance recorded	5	11
Consumer and Industrial [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	762	576
Unpaid principal, With no related allowance recorded	926	688
Average recorded Investment, With no related allowance recorded	669	494
Interest income Recognized, With no related allowance recorded	48	29
Recorded investment, With an allowance recorded	3,334	2,094
Unpaid principal, With an allowance recorded	3,385	2,117
Related allowance, With an allowance recorded	1,130	1,187
Average recorded Investment, With an allowance recorded	2,714	1,716
Interest income Recognized, With an allowance recorded	77	122
Consumer and Industrial [Member] | PNCI Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded		1
Unpaid principal, With no related allowance recorded		1
Average recorded Investment, With no related allowance recorded	1	4
Construction [Member] | Residential [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded investment, With no related allowance recorded	11	4
Unpaid principal, With no related allowance recorded	16	65
Average recorded Investment, With no related allowance recorded	7	1,202
Average recorded Investment, With an allowance recorded		141
Construction [Member] | Commercial [Member] | Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded Investment, With no related allowance recorded		50
Construction [Member] | Commercial [Member] | PNCI Loans [Member]
Financing Receivable, Impaired [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