Investment Securities - Unrealized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available-for-sale securities, Duration of Unrealized Loss Position, Less than 12 Month, Fair Value	$ 733,646	$ 103,226
Available-for-sale Securities, Duration of Unrealized Loss Position, Less than 12 Month, Gross Unrealized Loss	(10,668)	(847)
Available-for-sale securities, Duration of Unrealized Loss Position, 12 Month or Longer, Fair Value	5,909
Available-for-sale Securities, Duration of Unrealized Loss Position, 12 Month or Longer, Gross Unrealized Loss	(329)
Available-for-sale securities, Total, Fair Value	739,555	103,226
Available-for-sale securities, Total, Unrealized Loss	(10,997)	(847)
Obligations of U.S. government corporations and agencies [Member]
Available-for-sale securities, Duration of Unrealized Loss Position, Less than 12 Month, Fair Value	55,017
Available-for-sale Securities, Duration of Unrealized Loss Position, Less than 12 Month, Gross Unrealized Loss	(676)
Available-for-sale securities, Total, Fair Value	55,017
Available-for-sale securities, Total, Unrealized Loss	(676)
Mortgage-Backed Securities [Member]
Available-for-sale securities, Duration of Unrealized Loss Position, Less than 12 Month, Fair Value	180,687
Available-for-sale Securities, Duration of Unrealized Loss Position, Less than 12 Month, Gross Unrealized Loss	(2,262)
Available-for-sale securities, Total, Fair Value	180,687
Available-for-sale securities, Total, Unrealized Loss	(2,262)
Mortgage-backed - residential [Member]
Available-for-sale securities, Duration of Unrealized Loss Position, Less than 12 Month, Fair Value		26,361
Available-for-sale Securities, Duration of Unrealized Loss Position, Less than 12 Month, Gross Unrealized Loss		(247)
Available-for-sale securities, Total, Fair Value		26,361
Available-for-sale securities, Total, Unrealized Loss		(247)
Collateralized mortgage obligations [Member]
Available-for-sale securities, Duration of Unrealized Loss Position, Less than 12 Month, Fair Value	213,446	5,161
Available-for-sale Securities, Duration of Unrealized Loss Position, Less than 12 Month, Gross Unrealized Loss	(2,073)	(160)
Available-for-sale securities, Total, Fair Value	213,446	5,161
Available-for-sale securities, Total, Unrealized Loss	(2,073)	(160)
Corporate bonds [Member]
Available-for-sale securities, Duration of Unrealized Loss Position, Less than 12 Month, Fair Value	15,409	12,177
Available-for-sale Securities, Duration of Unrealized Loss Position, Less than 12 Month, Gross Unrealized Loss	(101)	(146)
Available-for-sale securities, Duration of Unrealized Loss Position, 12 Month or Longer, Fair Value	505
Available-for-sale Securities, Duration of Unrealized Loss Position, 12 Month or Longer, Gross Unrealized Loss	(6)
Available-for-sale securities, Total, Fair Value	15,914	12,177
Available-for-sale securities, Total, Unrealized Loss	(107)	(146)
Obligations of state and political subdivisions [Member]
Available-for-sale securities, Duration of Unrealized Loss Position, Less than 12 Month, Fair Value	153,264	41,088
Available-for-sale Securities, Duration of Unrealized Loss Position, Less than 12 Month, Gross Unrealized Loss	(4,705)	(196)
Available-for-sale securities, Duration of Unrealized Loss Position, 12 Month or Longer, Fair Value	5,404
Available-for-sale Securities, Duration of Unrealized Loss Position, 12 Month or Longer, Gross Unrealized Loss	(323)
Available-for-sale securities, Total, Fair Value	158,668	41,088
Available-for-sale securities, Total, Unrealized Loss	(5,028)	(196)
Asset-backed securities [Member]
Available-for-sale securities, Duration of Unrealized Loss Position, Less than 12 Month, Fair Value	115,823	18,439
Available-for-sale Securities, Duration of Unrealized Loss Position, Less than 12 Month, Gross Unrealized Loss	(851)	(98)
Available-for-sale securities, Total, Fair Value	115,823	18,439
Available-for-sale securities, Total, Unrealized Loss	$ (851)	$ (98)