Loans and Allowance for Credit Losses on Loans (Credit Risk Exposure Indicators by Portfolio Segment) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 3,219,822	$ 3,095,023	$ 3,026,222
Pass (Grades 1 – 6)
Financing Receivable, Recorded Investment [Line Items]
Loans		2,696,045
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans		336,401
Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans		34,859
Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans		25,568
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans		2,150
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,054,798	1,070,374	992,866
Residential real estate | Pass (Grades 1 – 6)
Financing Receivable, Recorded Investment [Line Items]
Loans		1,062,825
Residential real estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans		473
Residential real estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans		7,076
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans		1,243,397	1,269,533
Commercial real estate | Pass (Grades 1 – 6)
Financing Receivable, Recorded Investment [Line Items]
Loans		1,196,683
Commercial real estate | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans		31,753
Commercial real estate | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans		14,961
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	381,494	442,701	415,436
Commercial | Pass (Grades 1 – 6)
Financing Receivable, Recorded Investment [Line Items]
Loans		436,537
Commercial | Special Mention (Grade 7)
Financing Receivable, Recorded Investment [Line Items]
Loans		2,633
Commercial | Substandard (Grade 8)
Financing Receivable, Recorded Investment [Line Items]
Loans		3,531
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	258,573	312,779	327,763
Home equity | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans		310,653
Home equity | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans		2,126
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 20,392	25,772	$ 20,624
Consumer | Performing
Financing Receivable, Recorded Investment [Line Items]
Loans		25,748
Consumer | Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 24