Allowance for Loan Losses - Recorded Investment in Consumer Loan Classes by Performing and Nonperforming Status (Detail) - Consumer - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,244,649	$ 1,190,735
Percentage of Total	100.00%	100.00%
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,230,250	$ 1,182,104
Percentage of Total	98.80%	99.30%
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 14,399	$ 8,631
Percentage of Total	1.20%	0.70%
Residential Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 692,574	$ 639,372
Percentage of Total	100.00%	100.00%
Residential Mortgage | Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 681,174	$ 633,743
Percentage of Total	98.40%	99.10%
Residential Mortgage | Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 11,400	$ 5,629
Percentage of Total	1.60%	0.90%
Home Equity
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 483,935	$ 470,845
Percentage of Total	100.00%	100.00%
Home Equity | Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 480,980	$ 467,943
Percentage of Total	99.40%	99.40%
Home Equity | Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 2,955	$ 2,902
Percentage of Total	0.60%	0.60%
Installment and Other Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 62,288	$ 73,939
Percentage of Total	100.00%	100.00%
Installment and Other Consumer | Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 62,244	$ 73,839
Percentage of Total	99.90%	99.80%
Installment and Other Consumer | Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 44	$ 100
Percentage of Total	0.10%	0.20%
Consumer Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 5,852	$ 6,579
Percentage of Total	100.00%	100.00%
Consumer Construction | Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 5,852	$ 6,579
Percentage of Total	100.00%	100.00%
Consumer Construction | Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 0	$ 0
Percentage of Total	0.00%	0.00%