Securities - Schedule of Available-for-Sales Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,072,498	$ 1,599,894
Gross Unrealized Gains	18,021	30,773
Gross Unrealized Losses	23,592	3,474
Fair Value	2,066,927	1,627,193
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	140,373
Gross Unrealized Gains	2
Gross Unrealized Losses	1,447
Fair Value	138,928
Obligations of U.S. Government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	813,833	599,652
Gross Unrealized Gains	6,001	9,820
Gross Unrealized Losses	9,491	1,992
Fair Value	810,343	607,480
Obligations of U.S. states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	107,912	126,642
Gross Unrealized Gains	2,144	3,144
Gross Unrealized Losses	145	40
Fair Value	109,911	129,746
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	88,135	179,538
Gross Unrealized Gains	1,607	3,216
Gross Unrealized Losses	422	646
Fair Value	89,320	182,108
U.S. Government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	919,745	691,562
Gross Unrealized Gains	8,267	14,593
Gross Unrealized Losses	12,008	675
Fair Value	916,004	705,480
U.S. corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,500	2,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	79	121
Fair Value	$ 2,421	$ 2,379