Securities (Narrative) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) security $ / shares shares	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	22	54
Investment securities, pledged as collateral for public deposits	$ 254,486,000	$ 260,826,000
FHLB stock and FRB stock, cost	37,952,000	33,380,000
FHLB, cost	20,329,000	15,789,000
FRB stock	$ 17,623,000	$ 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