Investment Securities - Schedule of contractual maturity of debt securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 1,187,499	$ 1,028,883
Debt Securities, Available-for-sale	1,209,701	1,003,421
Obligations of States and Political Subdivisions
Investment [Line Items]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost	3,984
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value	$ 4,135
Debt Securities, Available-for-sale, Maturity, after Five Through Ten Years, Weighted Average Yield	3.04%
Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost	$ 298,944
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value	$ 316,356
Debt Securities, Available-for-sale, Maturity, after 10 Years, Weighted Average Yield	3.69%
Debt Securities, Available-for-sale, Amortized Cost	$ 302,928
Debt Securities, Available-for-sale	$ 320,491
Available for Sale Securities Weighted Avg Yield	3.68%
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 884,571	1,028,883
Debt Securities, Available-for-sale	$ 889,210	$ 1,003,421
Available for Sale Securities Weighted Avg Yield	2.37%

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