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Investment Securities - Narrative (Details)	Dec. 31, 2020 USD ($) instrument	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Fair value of investments	$ 80,881,000	$ 395,416,000
Unrealized losses on available for sale securities	349,000	2,211,000
Unrealized losses in held to maturity portfolios	252,000	545,000
Carrying value of securities pledged as collateral	890,025,000	503,427,000	$ 416,155,000
Securities sold under repurchase agreements	167,265,000	182,856,000
Investments in Debt and Equity Securities, Reported at Less than Historical Cost
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Historical cost	81,482,000	398,172,000
Fair value of investments	$ 80,881,000	$ 395,416,000
Percent of the Corporation's available for sale and held to maturity portfolio	2.60%	15.20%
U.S. Government-Sponsored Mortgage-backed Securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Unrealized losses on available for sale securities	$ 103,000	$ 1,404,000
Available-for-sale number of securities in unrealized loss positions | instrument	5
Unrealized losses in held to maturity portfolios	$ 107,000	401,000
Held-to-maturity, number of securities in unrealized loss positions | instrument	3
State and municipal securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Unrealized losses on available for sale securities	$ 246,000	807,000
Available-for-sale number of securities in unrealized loss positions | instrument	4
Unrealized losses in held to maturity portfolios	$ 32,000	107,000
Held-to-maturity, number of securities in unrealized loss positions | instrument	2
U.S. Government-sponsored agency securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Unrealized losses on available for sale securities	$ 0	0
Unrealized losses in held to maturity portfolios	$ 113,000	$ 37,000
Held-to-maturity, number of securities in unrealized loss positions | instrument	2

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