Allowance for Loan Losses - Recorded Investment in Consumer Loan Classes by Performing and Nonperforming Status (Details) - Consumer - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,246,281	$ 1,257,855
Percentage of Total	100.00%	100.00%
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,235,732	$ 1,246,904
Percentage of Total	99.20%	99.10%
Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 10,549	$ 10,951
Percentage of Total	0.80%	0.90%
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 699,867	$ 698,774
Percentage of Total	100.00%	100.00%
Residential mortgage | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 693,146	$ 691,609
Percentage of Total	99.00%	99.00%
Residential mortgage | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 6,721	$ 7,165
Percentage of Total	1.00%	1.00%
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 472,451	$ 487,326
Percentage of Total	100.00%	100.00%
Home equity | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 468,668	$ 483,611
Percentage of Total	99.20%	99.20%
Home equity | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 3,783	$ 3,715
Percentage of Total	0.80%	0.80%
Installment and other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 67,542	$ 67,204
Percentage of Total	100.00%	100.00%
Installment and other consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 67,497	$ 67,133
Percentage of Total	99.90%	99.90%
Installment and other consumer | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 45	$ 71
Percentage of Total	0.10%	0.10%
Consumer construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 6,421	$ 4,551
Percentage of Total	100.00%	100.00%
Consumer construction | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 6,421	$ 4,551
Percentage of Total	100.00%	100.00%
Consumer construction | Nonperforming
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 0	$ 0
Percentage of Total	0.00%	0.00%