Allowance for Loan Losses - Presentation of Credit Quality Indicators (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 2,712,226	$ 2,522,937	$ 2,469,566
Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	57,892	46,135	46,067
Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	61,295	74,774	64,006
Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	301,884	322,492	331,689
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	31,611	32,429	33,027
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,273,536	1,988,745
Originated Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	57,203	31,778
Originated Loans [Member] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	52,370	66,285
Originated Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	272,275	285,419
Originated Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	28,982	28,998
PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	411,807	493,988
PNCI Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	146	13,636
PNCI Loans [Member] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	8,925	8,489
PNCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	24,378	29,335
PNCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,568	3,367
PCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	26,883	40,204
PCI Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	543	721
PCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	5,231	7,738
PCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	61	64
C&I [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	217,110	194,913	199,330
C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	199,947	170,320
C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,015	19,744
C&I [Member] | PCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	4,148	4,849
Pass [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,223,567	1,918,006
Pass [Member] | Originated Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	57,203	31,440
Pass [Member] | Originated Loans [Member] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	52,062	66,285
Pass [Member] | Originated Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	265,949	275,251
Pass [Member] | Originated Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	28,532	28,339
Pass [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	393,620	472,952
Pass [Member] | PNCI Loans [Member] | Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	146	13,636
Pass [Member] | PNCI Loans [Member] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	8,925	8,489
Pass [Member] | PNCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	22,826	27,378
Pass [Member] | PNCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,477	3,164
Pass [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	193,411	166,559
Pass [Member] | C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,013	19,666
Special Mention [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	23,375	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] | Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	308
Special Mention [Member] | Originated Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,269	2,494
Special Mention [Member] | Originated Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	302	415
Special Mention [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	8,377	11,994
Special Mention [Member] | PNCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	415	445
Special Mention [Member] | PNCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	63	74
Special Mention [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,463	1,037
Special Mention [Member] | C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2
Substandard [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	26,594	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	4,057	7,674
Substandard [Member] | Originated Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	148	244
Substandard [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	9,810	9,042
Substandard [Member] | PNCI Loans [Member] | Home Equity Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,137	1,512
Substandard [Member] | PNCI Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	28	129
Substandard [Member] | C&I [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,073	2,724
Substandard [Member] | C&I [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans		78
Home Equity Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	43,521	40,362	38,365
Home Equity Loans [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	38,265	34,717
Home Equity Loans [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,702	4,018
Home Equity Loans [Member] | PCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,554	1,627
Home Equity Loans [Member] | Pass [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	34,248	31,427
Home Equity Loans [Member] | Pass [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,538	3,789
Home Equity Loans [Member] | Special Mention [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	833	1,027
Home Equity Loans [Member] | Special Mention [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	48	80
Home Equity Loans [Member] | Substandard [Member] | Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,184	2,263
Home Equity Loans [Member] | Substandard [Member] | PNCI Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	116	149
RE Mortgage [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	313,069	314,265	302,105
RE Mortgage [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,685,844	1,497,567	$ 1,454,977
RE Mortgage [Member] | Originated Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	225,179	207,585
RE Mortgage [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,399,315	1,163,643
RE Mortgage [Member] | PNCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	86,525	104,535
RE Mortgage [Member] | PNCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	272,548	310,864
RE Mortgage [Member] | PCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,365	2,145
RE Mortgage [Member] | PCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,981	23,060
RE Mortgage [Member] | Pass [Member] | Originated Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	219,263	199,837
RE Mortgage [Member] | Pass [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,372,899	1,118,868
RE Mortgage [Member] | Pass [Member] | PNCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	83,847	102,895
RE Mortgage [Member] | Pass [Member] | PNCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	258,848	293,935
RE Mortgage [Member] | Special Mention [Member] | Originated Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,005	2,018
RE Mortgage [Member] | Special Mention [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	14,195	10,321
RE Mortgage [Member] | Special Mention [Member] | PNCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,571	600
RE Mortgage [Member] | Special Mention [Member] | PNCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	6,278	10,795
RE Mortgage [Member] | Substandard [Member] | Originated Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,911	5,730
RE Mortgage [Member] | Substandard [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	12,221	34,454
RE Mortgage [Member] | Substandard [Member] | PNCI Loans [Member] | Residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,107	1,040
RE Mortgage [Member] | Substandard [Member] | PNCI Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 7,422	$ 6,134