Investment Securities - Schedule of contractual maturity of debt securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 1,007,834	$ 1,187,499
Debt Securities, Available-for-sale	1,059,341	1,209,701
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	66,449
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value	$ 72,860
Debt Securities, Available-for-sale, Maturity, after Five Through Ten Years, Weighted Average Yield	3.80%
Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost	$ 212,796
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value	$ 232,358
Debt Securities, Available-for-sale, Maturity, after 10 Years, Weighted Average Yield	3.67%
Debt Securities, Available-for-sale, Amortized Cost	$ 279,245	302,928
Debt Securities, Available-for-sale	$ 305,218	320,491
Available for Sale Securities Weighted Avg Yield	3.70%
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 726,589	884,571
Debt Securities, Available-for-sale	$ 752,109	$ 889,210
Available for Sale Securities Weighted Avg Yield	2.14%
Corporate Debt Securities
Investment [Line Items]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost	$ 2,000
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value	$ 2,014
Debt Securities, Available-for-sale, Maturity, after Five Through Ten Years, Weighted Average Yield	4.00%
Debt Securities, Available-for-sale, Amortized Cost	$ 2,000
Debt Securities, Available-for-sale	$ 2,014

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Amortized cost of 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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Amount of 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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