Allowance for Loan Losses - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	$ 56,681	$ 73,890	$ 66,241
Unpaid principal, With no related allowance recorded	69,782	90,972	82,489
Average recorded Investment, With no related allowance recorded	61,460	75,159	71,116
Interest income Recognized, With no related allowance recorded	1,083	3,334	4,326
Recorded investment, With an allowance recorded	11,100	15,439	12,855
Unpaid principal, With an allowance recorded	11,916	17,834	13,896
Related allowance, With an allowance recorded	3,519	3,955	3,558
Average recorded Investment, With an allowance recorded	11,978	15,950	15,050
Interest income Recognized, With an allowance recorded	299	784	707
PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	1,071	1,142	1,562
Unpaid principal, With no related allowance recorded	3,331	3,295	3,825
Average recorded Investment, With no related allowance recorded	1,317	1,489	1,421
Interest income Recognized, With no related allowance recorded	13	177	271
Recorded investment, With an allowance recorded	1,194	747	578
Unpaid principal, With an allowance recorded	1,207	773	599
Related allowance, With an allowance recorded	573	515	417
Average recorded Investment, With an allowance recorded	886	729	716
Interest income Recognized, With an allowance recorded	36	35	32
RE Mortgage [Member] | Residential [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	3,576	4,195	4,366
Unpaid principal, With no related allowance recorded	5,671	6,320	6,489
Average recorded Investment, With no related allowance recorded	3,971	3,911	4,123
Interest income Recognized, With no related allowance recorded	29	246	336
Recorded investment, With an allowance recorded	2,838	2,468	2,630
Unpaid principal, With an allowance recorded	3,017	2,510	2,689
Related allowance, With an allowance recorded	745	480	648
Average recorded Investment, With an allowance recorded	2,734	2,304	2,245
Interest income Recognized, With an allowance recorded	59	93	124
RE Mortgage [Member] | Residential [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	299		148
Unpaid principal, With no related allowance recorded	306		158
Average recorded Investment, With no related allowance recorded	224		37
Interest income Recognized, With no related allowance recorded	12		11
Recorded investment, With an allowance recorded	429	350	198
Unpaid principal, With an allowance recorded	442	366	207
Related allowance, With an allowance recorded	158	193	128
Average recorded Investment, With an allowance recorded	313	276	275
Interest income Recognized, With an allowance recorded	6	18	12
RE Mortgage [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	46,412	61,418	53,352
Unpaid principal, With no related allowance recorded	49,609	67,314	58,894
Average recorded Investment, With no related allowance recorded	49,882	61,375	58,205
Interest income Recognized, With no related allowance recorded	999	2,644	3,361
Recorded investment, With an allowance recorded	3,344	6,990	5,296
Unpaid principal, With an allowance recorded	3,489	7,670	5,659
Related allowance, With an allowance recorded	304	1,293	1,084
Average recorded Investment, With an allowance recorded	4,320	5,568	6,077
Interest income Recognized, With an allowance recorded	133	388	287
RE Mortgage [Member] | Commercial [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	419	800	1,139
Unpaid principal, With no related allowance recorded	2,636	2,893	3,323
Average recorded Investment, With no related allowance recorded	779	1,088	1,005
Interest income Recognized, With no related allowance recorded		154	233
Recorded investment, With an allowance recorded	147	165	149
Unpaid principal, With an allowance recorded	147	165	149
Related allowance, With an allowance recorded	109	133	114
Average recorded Investment, With an allowance recorded	148	292	250
Interest income Recognized, With an allowance recorded	6	7	9
Home equity lines of credit [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	2,655	3,938	3,710
Unpaid principal, With no related allowance recorded	5,645	7,445	7,299
Average recorded Investment, With no related allowance recorded	3,182	4,543	4,410
Interest income Recognized, With no related allowance recorded	14	268	352
Recorded investment, With an allowance recorded	3,291	3,232	2,779
Unpaid principal, With an allowance recorded	3,653	3,703	3,053
Related allowance, With an allowance recorded	1,764	1,350	968
Average recorded Investment, With an allowance recorded	3,035	3,722	3,064
Interest income Recognized, With an allowance recorded	49	109	146
Home equity lines of credit [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	314	290	227
Unpaid principal, With no related allowance recorded	337	342	287
Average recorded Investment, With no related allowance recorded	270	367	333
Interest income Recognized, With no related allowance recorded		19	21
Recorded investment, With an allowance recorded	473	204	203
Unpaid principal, With an allowance recorded	473	214	215
Related allowance, With an allowance recorded	237	179	172
Average recorded Investment, With an allowance recorded	338	121	162
Interest income Recognized, With an allowance recorded	16	9	10
Home equity loans [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	657	442	552
Unpaid principal, With no related allowance recorded	1,082	1,131	1,249
Average recorded Investment, With no related allowance recorded	604	415	463
Interest income Recognized, With no related allowance recorded	1	21	36
Recorded investment, With an allowance recorded	239	109	226
Unpaid principal, With an allowance recorded	323	161	291
Related allowance, With an allowance recorded	213	49	169
Average recorded Investment, With an allowance recorded	233	126	141
Interest income Recognized, With an allowance recorded	3	8	18
Auto Indirect [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	23	61	55
Unpaid principal, With no related allowance recorded	60	135	123
Average recorded Investment, With no related allowance recorded	39	120	93
Interest income Recognized, With no related allowance recorded		10	12
Recorded investment, With an allowance recorded		5	4
Unpaid principal, With an allowance recorded		7	6
Related allowance, With an allowance recorded		2	1
Average recorded Investment, With an allowance recorded	2	19	12
Interest income Recognized, With an allowance recorded			1
Other Consumer [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	18	19	16
Unpaid principal, With no related allowance recorded	25	32	21
Average recorded Investment, With no related allowance recorded	17	19	18
Interest income Recognized, With no related allowance recorded		2	1
Recorded investment, With an allowance recorded		9	10
Unpaid principal, With an allowance recorded		10	10
Related allowance, With an allowance recorded		3	5
Average recorded Investment, With an allowance recorded	5	12	7
Interest income Recognized, With an allowance recorded		1	2
Other Consumer [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	31	38	36
Unpaid principal, With no related allowance recorded	44	46	45
Average recorded Investment, With no related allowance recorded	34	30	39
Interest income Recognized, With no related allowance recorded		4	5
Recorded investment, With an allowance recorded	145	28	28
Unpaid principal, With an allowance recorded	145	28	28
Related allowance, With an allowance recorded	69	10	3
Average recorded Investment, With an allowance recorded	87	40	29
Interest income Recognized, With an allowance recorded	8	1	1
C&I [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	789	1,161	1,648
Unpaid principal, With no related allowance recorded	806	1,182	1,665
Average recorded Investment, With no related allowance recorded	1,218	2,802	2,154
Interest income Recognized, With no related allowance recorded	37	61	113
Recorded investment, With an allowance recorded	1,105	2,158	1,517
Unpaid principal, With an allowance recorded	1,151	3,063	1,616
Related allowance, With an allowance recorded	433	678	585
Average recorded Investment, With an allowance recorded	1,311	2,519	1,817
Interest income Recognized, With an allowance recorded	41	155	95
C&I [Member] | PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	8	14	12
Unpaid principal, With no related allowance recorded	8	14	12
Average recorded Investment, With no related allowance recorded	10	4	7
Interest income Recognized, With no related allowance recorded	1		1
Construction [Member] | Residential [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	2,437	2,588	2,473
Unpaid principal, With no related allowance recorded	6,686	7,345	6,611
Average recorded Investment, With no related allowance recorded	2,455	1,837	1,567
Interest income Recognized, With no related allowance recorded		81	108
Recorded investment, With an allowance recorded	283	284	284
Unpaid principal, With an allowance recorded	283	284	284
Related allowance, With an allowance recorded	60	91	91
Average recorded Investment, With an allowance recorded	283	1,438	1,499
Interest income Recognized, With an allowance recorded	14	14	19
Construction [Member] | Commercial [Member] | Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment, With no related allowance recorded	114	68	69
Unpaid principal, With no related allowance recorded	198	68	138
Average recorded Investment, With no related allowance recorded	92	137	83
Interest income Recognized, With no related allowance recorded	3	1	7
Recorded investment, With an allowance recorded		184	109
Unpaid principal, With an allowance recorded		426	288
Related allowance, With an allowance recorded		9	7
Average recorded Investment, With an allowance recorded	55	242	188
Interest income Recognized, With an allowance recorded		$ 16	$ 15