Investments - Schedule of Available-for-sale Securities, at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 1,033,819	$ 842,158
Allowance for credit losses	(610)	(84)	$ (346)	$ (190)
Gross unrealized gains	8,573	3,014
Gross unrealized losses	(31,715)	(42,479)
Fair value	1,010,067	802,609
U.S. Treasury securities and obligations of U.S. government authorities and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized cost	454,042	496,731
Allowance for credit losses	0	0
Gross unrealized gains	1,791	515
Gross unrealized losses	(20,745)	(27,161)
Fair value	435,088	470,085
Obligations of state and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized cost	43,886	48,762
Allowance for credit losses	(1)	(1)	(1)	(3)
Gross unrealized gains	66	51
Gross unrealized losses	(2,414)	(3,353)
Fair value	41,537	45,459
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	507,055	260,961
Allowance for credit losses	(478)	(73)	(331)	(183)
Gross unrealized gains	6,714	2,445
Gross unrealized losses	(6,103)	(8,735)
Fair value	507,188	254,598
Asset backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	26,298	29,275
Allowance for credit losses	(131)	(10)	(14)	(1)
Gross unrealized gains	2	3
Gross unrealized losses	(2,349)	(3,082)
Fair value	23,820	26,186
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized cost	1,145	1,724
Allowance for credit losses	0	0
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	1,145	1,724
Obligations of foreign governments
Debt Securities, Available-for-sale [Line Items]
Amortized cost	1,393	4,705
Allowance for credit losses	0	0	$ 0	$ (3)
Gross unrealized gains	0	0
Gross unrealized losses	(104)	(148)
Fair value	$ 1,289	$ 4,557