Investment Securities - Amortized Cost of Debt Securities Held-to-Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized cost, held to maturity	$ 235,778	$ 284,563
AAA/AA/A
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized cost, held to maturity	235,778	284,563
BBB/BB/B
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized cost, held to maturity	0	0
Obligations of U.S. government agencies | AAA/AA/A
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized cost, held to maturity	226,925	273,667
Obligations of U.S. government agencies | BBB/BB/B
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized cost, held to maturity	0	0
Obligations of states and political subdivisions | AAA/AA/A
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized cost, held to maturity	8,853	10,896
Obligations of states and political subdivisions | BBB/BB/B
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized cost, held to maturity	$ 0	$ 0