Allowance for Loan Losses - Presentation of Credit Quality Indicators (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 2,653,630	$ 2,522,937	$ 2,393,762
Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	62,331	46,135	41,958
Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	87,321	74,774	57,658
Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	306,678	322,492	344,115
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32,434	32,429	33,101
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,175,609	1,988,745
Originated Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	48,608	31,778
Originated Loans [Member] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	78,200	66,285
Originated Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	273,849	285,419
Originated Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	29,623	28,998
PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	447,677	493,988
PNCI Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,174	13,636
PNCI Loans [Member] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	9,121	8,489
PNCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	26,579	29,335
PNCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,748	3,367
PCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	30,344	40,204
PCI Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	549	721
PCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	6,250	7,738
PCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	63	64
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	209,840	194,913	195,791
C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	189,494	170,320
C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	16,062	19,744
C&I [Member] | PCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,284	4,849
Pass [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,122,098	1,918,006
Pass [Member] | Originated Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	48,608	31,440
Pass [Member] | Originated Loans [Member] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	78,200	66,285
Pass [Member] | Originated Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	265,496	275,251
Pass [Member] | Originated Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	29,100	28,339
Pass [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	424,839	472,952
Pass [Member] | PNCI Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,174	13,636
Pass [Member] | PNCI Loans [Member] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	9,121	8,489
Pass [Member] | PNCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	25,075	27,378
Pass [Member] | PNCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,573	3,164
Pass [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	182,447	166,559
Pass [Member] | C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	15,995	19,666
Special Mention [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	22,427	17,646
Special Mention [Member] | Originated Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		334
Special Mention [Member] | Originated Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,335	2,494
Special Mention [Member] | Originated Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	357	415
Special Mention [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	9,196	11,994
Special Mention [Member] | PNCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	410	445
Special Mention [Member] | PNCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	57	74
Special Mention [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,049	1,037
Special Mention [Member] | C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	8
Substandard [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	31,084	53,093
Substandard [Member] | Originated Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		4
Substandard [Member] | Originated Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	6,018	7,674
Substandard [Member] | Originated Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	166	244
Substandard [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,642	9,042
Substandard [Member] | PNCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,094	1,512
Substandard [Member] | PNCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	118	129
Substandard [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,998	2,724
Substandard [Member] | C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	59	78
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	42,002	40,362	34,572
Home Equity Loans [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	36,517	34,717
Home Equity Loans [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,854	4,018
Home Equity Loans [Member] | PCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,631	1,627
Home Equity Loans [Member] | Pass [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	32,662	31,427
Home Equity Loans [Member] | Pass [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,691	3,789
Home Equity Loans [Member] | Special Mention [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,060	1,027
Home Equity Loans [Member] | Special Mention [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	74	80
Home Equity Loans [Member] | Substandard [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,795	2,263
Home Equity Loans [Member] | Substandard [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	89	149
RE Mortgage [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	318,206	314,265	291,488
RE Mortgage [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,594,818	1,497,567	$ 1,395,079
RE Mortgage [Member] | Originated Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	221,460	207,585
RE Mortgage [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,297,858	1,163,643
RE Mortgage [Member] | PNCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	95,121	104,535
RE Mortgage [Member] | PNCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	281,018	310,864
RE Mortgage [Member] | PCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,625	2,145
RE Mortgage [Member] | PCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	15,942	23,060
RE Mortgage [Member] | Pass [Member] | Originated Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	214,128	199,837
RE Mortgage [Member] | Pass [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,271,457	1,118,868
RE Mortgage [Member] | Pass [Member] | PNCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	93,348	102,895
RE Mortgage [Member] | Pass [Member] | PNCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	261,862	293,935
RE Mortgage [Member] | Special Mention [Member] | Originated Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,117	2,018
RE Mortgage [Member] | Special Mention [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	12,509	10,321
RE Mortgage [Member] | Special Mention [Member] | PNCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	540	600
RE Mortgage [Member] | Special Mention [Member] | PNCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	8,107	10,795
RE Mortgage [Member] | Substandard [Member] | Originated Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	5,215	5,730
RE Mortgage [Member] | Substandard [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,892	34,454
RE Mortgage [Member] | Substandard [Member] | PNCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,233	1,040
RE Mortgage [Member] | Substandard [Member] | PNCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 11,049	$ 6,134