Investment Securities - Narrative (Details) $ in Thousands	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Fair value of investments	$ 395,416	$ 932,577
Unrealized losses on available for sale securities	2,211	14,253
Unrealized losses in held to maturity portfolios	545	4,741
Carrying value of securities pledged as collateral	503,427	416,155	$ 475,999
Securities sold under repurchase agreements	182,856	116,691
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	398,172	951,571
Fair value of investments	$ 395,416	$ 932,577
Percent of the Corporation's available for sale and held to maturity portfolio	15.20%	57.10%
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	$ 1,404	$ 8,396
Available-for-sale number of securities in unrealized loss positions \| security	27
Unrealized losses in held to maturity portfolios	$ 401	3,323
Held-to-maturity, number of securities in unrealized loss positions \| security	15
State and municipal securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Unrealized losses on available for sale securities	$ 807	5,854
Available-for-sale number of securities in unrealized loss positions \| security	38
Unrealized losses in held to maturity portfolios	$ 107	872
Held-to-maturity, number of securities in unrealized loss positions \| security	18
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	3
Unrealized losses in held to maturity portfolios	$ 37	$ 545
Held-to-maturity, number of securities in unrealized loss positions \| security	3

Investment Historical Cost

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Percentage of Total Investment Portfolio, Fair Value

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Schedule of Available for sale Securities and Held to maturity Securities [Line Items]

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Securities, Continuous Unrealized Loss Position, Fair Value

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Securities Pledged as Collateral

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

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Amount of asset associated with funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price.

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