Investment Securities - Investments in Debt and Equity Securities Reported Less than Historical Cost (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Fair value	$ 58,130	$ 395,416
Investments reported at less than historical cost
Schedule of Investments [Line Items]
Historical cost	58,565	398,172
Fair value	58,130	395,416
Gross unrealized losses	$ 435	$ 2,756
Percent of the Corporation's investment portfolio	2.20%	15.20%