Investments - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 226,694	$ 722,676
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4,650	45,806
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,258,092	756,002
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	230,371	147,922
Debt Securities, Available-for-sale, Unrealized Loss Position	1,484,786	1,478,678
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	235,021	193,728
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	43,940	73,738
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	800	6,249
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	235,517	163,047
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	27,924	22,056
Debt Securities, Available-for-sale, Unrealized Loss Position	279,457	236,785
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	28,724	28,305
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	3,687	103,179
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	467	13,501
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	383,239	311,634
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	113,622	76,924
Debt Securities, Available-for-sale, Unrealized Loss Position	386,926	414,813
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	114,089	90,425
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	102,488	334,431
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,210	20,038
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	523,672	281,321
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	82,716	48,942
Debt Securities, Available-for-sale, Unrealized Loss Position	626,160	615,752
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	85,926	68,980
U.S. Treasury bills
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	12,640
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	1,110
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	7,452	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,298	0
Debt Securities, Available-for-sale, Unrealized Loss Position	7,452	12,640
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1,298	1,110
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	76,579	198,688
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	173	4,908
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	108,212	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,811	0
Debt Securities, Available-for-sale, Unrealized Loss Position	184,791	198,688
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 4,984	$ 4,908