Allowance for Loan Losses - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	$ 50,199	$ 63,560	$ 48,466
Unpaid principal, With no related allowance recorded	63,954	75,010	61,660
Average recorded Investment, With no related allowance recorded	49,332	68,975	57,354
Interest income Recognized, With no related allowance recorded	302	371	1,095
Recorded investment, With an allowance recorded	11,498	14,641	11,021
Unpaid principal, With an allowance recorded	12,302	19,810	11,863
Related allowance, With an allowance recorded	4,122	3,495	3,646
Average recorded Investment, With an allowance recorded	11,260	14,781	11,938
Interest income Recognized, With an allowance recorded	94	71	409
PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	1,205	1,325	1,124
Unpaid principal, With no related allowance recorded	3,647	3,520	3,433
Average recorded Investment, With no related allowance recorded	1,164	1,348	1,344
Interest income Recognized, With no related allowance recorded	1	8	14
Recorded investment, With an allowance recorded	2,124	774	1,636
Unpaid principal, With an allowance recorded	2,136	792	1,654
Related allowance, With an allowance recorded	570	446	621
Average recorded Investment, With an allowance recorded	1,879	714	1,107
Interest income Recognized, With an allowance recorded	18	4	48
RE Mortgage [Member] | Residential [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	3,360	4,349	3,287
Unpaid principal, With no related allowance recorded	5,330	6,532	5,138
Average recorded Investment, With no related allowance recorded	3,323	4,206	3,826
Interest income Recognized, With no related allowance recorded	8	14	38
Recorded investment, With an allowance recorded	3,402	2,457	2,724
Unpaid principal, With an allowance recorded	3,570	2,528	2,865
Related allowance, With an allowance recorded	915	502	797
Average recorded Investment, With an allowance recorded	3,063	2,353	2,677
Interest income Recognized, With an allowance recorded	22	13	91
RE Mortgage [Member] | Residential [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	389	84	343
Unpaid principal, With no related allowance recorded	488	84	353
Average recorded Investment, With no related allowance recorded	366	58	246
Interest income Recognized, With no related allowance recorded	1	2	14
Recorded investment, With an allowance recorded	635	432	834
Unpaid principal, With an allowance recorded	644	443	852
Related allowance, With an allowance recorded	73	164	177
Average recorded Investment, With an allowance recorded	734	334	516
Interest income Recognized, With an allowance recorded	2	2	8
RE Mortgage [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	40,094	53,996	38,477
Unpaid principal, With no related allowance recorded	43,898	59,159	41,949
Average recorded Investment, With no related allowance recorded	39,286	57,403	45,915
Interest income Recognized, With no related allowance recorded	283	340	995
Recorded investment, With an allowance recorded	3,281	4,599	2,943
Unpaid principal, With an allowance recorded	3,432	5,240	3,101
Related allowance, With an allowance recorded	598	855	302
Average recorded Investment, With an allowance recorded	3,112	5,773	4,119
Interest income Recognized, With an allowance recorded	40	25	144
RE Mortgage [Member] | Commercial [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	313	870	366
Unpaid principal, With no related allowance recorded	2,601	3,044	2,620
Average recorded Investment, With no related allowance recorded	339	905	753
Recorded investment, With an allowance recorded	835	148	146
Unpaid principal, With an allowance recorded	838	149	146
Related allowance, With an allowance recorded	201	113	108
Average recorded Investment, With an allowance recorded	490	157	148
Interest income Recognized, With an allowance recorded	10	2	8
Home equity lines of credit [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	2,631	3,386	3,001
Unpaid principal, With no related allowance recorded	5,791	6,833	6,094
Average recorded Investment, With no related allowance recorded	2,816	3,972	3,355
Interest income Recognized, With no related allowance recorded		2	26
Recorded investment, With an allowance recorded	2,808	3,214	3,185
Unpaid principal, With an allowance recorded	3,077	3,449	3,533
Related allowance, With an allowance recorded	1,636	1,228	1,769
Average recorded Investment, With an allowance recorded	2,997	3,057	2,982
Interest income Recognized, With an allowance recorded	12	14	71
Home equity lines of credit [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	414	326	346
Unpaid principal, With no related allowance recorded	450	336	374
Average recorded Investment, With no related allowance recorded	380	339	287
Interest income Recognized, With no related allowance recorded		6	(1)
Recorded investment, With an allowance recorded	437	166	436
Unpaid principal, With an allowance recorded	437	172	436
Related allowance, With an allowance recorded	221	166	205
Average recorded Investment, With an allowance recorded	436	195	319
Interest income Recognized, With an allowance recorded	4		20
Home equity loans [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	870	541	750
Unpaid principal, With no related allowance recorded	1,335	921	1,187
Average recorded Investment, With no related allowance recorded	810	483	651
Interest income Recognized, With no related allowance recorded			6
Recorded investment, With an allowance recorded	464	234	504
Unpaid principal, With an allowance recorded	566	300	597
Related allowance, With an allowance recorded	337	178	284
Average recorded Investment, With an allowance recorded	484	170	365
Interest income Recognized, With an allowance recorded	1	1	13
Home equity loans [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	25		25
Unpaid principal, With no related allowance recorded	25		25
Average recorded Investment, With no related allowance recorded	25		12
Auto Indirect [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	10	45	14
Unpaid principal, With no related allowance recorded	30	82	49
Average recorded Investment, With no related allowance recorded	12	66	35
Recorded investment, With an allowance recorded	4	4	4
Unpaid principal, With an allowance recorded	6	5	6
Related allowance, With an allowance recorded	1	1
Average recorded Investment, With an allowance recorded	4	7	4
Other Consumer [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	19	32	25
Unpaid principal, With no related allowance recorded	23	37	32
Average recorded Investment, With no related allowance recorded	22	21	21
Interest income Recognized, With no related allowance recorded			1
Recorded investment, With an allowance recorded	43	5	41
Unpaid principal, With an allowance recorded	53	6	41
Related allowance, With an allowance recorded	17	1	11
Average recorded Investment, With an allowance recorded	42	7	25
Other Consumer [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	59	34	37
Unpaid principal, With no related allowance recorded	78	45	54
Average recorded Investment, With no related allowance recorded	48	37	36
Recorded investment, With an allowance recorded	217	28	220
Unpaid principal, With an allowance recorded	217	28	220
Related allowance, With an allowance recorded	75	3	131
Average recorded Investment, With an allowance recorded	219	28	124
Interest income Recognized, With an allowance recorded	2		12
C&I [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	748	1,105	412
Unpaid principal, With no related allowance recorded	776	1,120	433
Average recorded Investment, With no related allowance recorded	580	1,370	1,030
Interest income Recognized, With no related allowance recorded	11	15	26
Recorded investment, With an allowance recorded	1,214	1,421	1,338
Unpaid principal, With an allowance recorded	1,316	1,509	1,438
Related allowance, With an allowance recorded	559	626	423
Average recorded Investment, With an allowance recorded	1,276	1,766	1,428
Interest income Recognized, With an allowance recorded	15	13	71
C&I [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	5	11	7
Unpaid principal, With no related allowance recorded	5	11	7
Average recorded Investment, With no related allowance recorded	6	9	10
Interest income Recognized, 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	2,373	87	2,401
Unpaid principal, With no related allowance recorded	6,585	225	6,588
Average recorded Investment, With no related allowance recorded	2,387	1,415	2,437
Recorded investment, With an allowance recorded	282	2,707	282
Unpaid principal, With an allowance recorded	282	6,773	282
Related allowance, With an allowance recorded	59	104	60
Average recorded Investment, With an allowance recorded	282	1,497	283
Interest income Recognized, With an allowance recorded	4	5	19
Construction [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	94	19	99
Unpaid principal, With no related allowance recorded	186	101	190
Average recorded Investment, With no related allowance recorded	96	39	84
Interest income Recognized, With no related allowance recorded			3
Average recorded Investment, With an allowance recorded		$ 151	$ 55