Securities (Narrative) (Details)	9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) security $ / shares shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) security
Debt and Equity Securities, FV-NI [Line Items]
Private mortgage-backed security fair value	$ 1,000,000.0		$ 1,100,000
Other than temporary impairment losses	$ 0		$ 0
Number of securities held in an unrealized loss position | security	31		54
Investment securities, pledged as collateral for public deposits	$ 414,668,000		$ 260,826,000
Proceeds from sales of securities available for sale	219,697,000	$ 39,797,000
Gain from sales of securities	8,024,000	$ 97,000
FHLB stock and FRB stock, cost	23,527,000		33,380,000
FHLB, cost	5,855,000		15,789,000
FRB stock	$ 17,672,000		$ 17,591,000
Visa, Inc | Common Class B
Debt and Equity Securities, FV-NI [Line Items]
Stock owned (in shares) | shares	12,356
Visa, Inc | Common Class A
Debt and Equity Securities, FV-NI [Line Items]
Conversion price (in dollars per share) | $ / shares	$ 1.62
Conversion of stock (in shares) | shares	20,051