Investments - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 691,876	$ 75,062
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8,249	357
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,204	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	33	0
Debt Securities, Available-for-sale, Unrealized Loss Position	694,080	75,062
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	8,282	357
Obligations of U.S. Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	102,905	4,997
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	665	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	102,905	4,997
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	665	3
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	323,227	4,079
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4,871	33
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	557	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	13	0
Debt Securities, Available-for-sale, Unrealized Loss Position	323,784	4,079
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	4,884	33
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	205,761	65,986
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,710	321
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,647	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	20	0
Debt Securities, Available-for-sale, Unrealized Loss Position	207,408	65,986
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	2,730	$ 321
U.S. Treasury bills
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	59,983
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	59,983
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 3

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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