Allowance for Loan and Lease Loss and Credit Quality (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($) risk_code	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) risk_code	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Unallocated Allowance | $			$ 0		$ 0
Financing receivables modified as troubled debt restructurings within the previous 12 months for which there was a payment default | $	$ 0	$ 0	$ 0	$ 118
Homogeneous | Minimum
Financing Receivable, Allowance for Credit Losses [Line Items]
Duration of time account is past due before risk rating is applied			30 days
Restructured Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired loans | $	$ 14,500		$ 14,500		32,200
Percentage of loan collateral balance			100.00%
Available commitments for troubled debt restructurings outstanding | $			$ 52		$ 917
Minimal Risk | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	1		1
Loss | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	10		10
Loss | Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	10		10
Loss | Homogeneous | Minimum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			180 days
Loss | Homogeneous Retail
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	10		10
Loss | Homogeneous Retail | Minimum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			120 days
Loss | Homogeneous Retail | Minimum | Closed-End Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			120 days
Low Risk | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	2		2
Modest Risk | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	3		3
Average Risk | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	4		4
Acceptable Risk | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	5		5
Pass/Watch | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	6		6
Special Mention | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	7		7
Special Mention | Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	7		7
Special Mention | Homogeneous | Minimum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			30 days
Special Mention | Homogeneous | Maximum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			59 days
Special Mention | Homogeneous Retail | Minimum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			30 days
Special Mention | Homogeneous Retail | Maximum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			89 days
Substandard | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	8		8
Substandard | Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	8		8
Substandard | Homogeneous | Minimum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			60 days
Substandard | Homogeneous | Maximum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			89 days
Substandard | Homogeneous Retail
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	8		8
Substandard | Homogeneous Retail | Minimum | Open-End Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			90 days
Substandard | Homogeneous Retail | Minimum | Closed-End Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			90 days
Substandard | Homogeneous Retail | Maximum | Open-End Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			180 days
Substandard | Homogeneous Retail | Maximum | Closed-End Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			120 days
Doubtful | Non-Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	9		9
Doubtful | Homogeneous
Financing Receivable, Allowance for Credit Losses [Line Items]
Internal risk rating code	9		9
Doubtful | Homogeneous | Minimum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			90 days
Doubtful | Homogeneous | Maximum
Financing Receivable, Allowance for Credit Losses [Line Items]
Days past due on account for qualifying credit quality indicator			179 days