Investments - Schedule of Changes in Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 528,447	$ 705,193	$ 798,973
Included in realized gains / losses	0	0	(3,594)
Included in other comprehensive income	(3,689)	(105,156)	(8,308)
Acquisitions	0	0	25,000
Sales	0	0	(26,064)
Amortization	4,724	4,526	4,514
Other	(32,603)	(76,116)	(85,328)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Ending Balance	$ 496,879	$ 528,447	$ 705,193
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Realized gain (loss)—investments	Realized gain (loss)—investments	Realized gain (loss)—investments
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]		Attributable to Parent Company	Attributable to Parent Company
Asset- backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	$ 0	$ 0	$ 12,870
Included in realized gains / losses			(82)
Included in other comprehensive income			63
Acquisitions			0
Sales			(12,851)
Amortization			0
Other			0
Transfers into Level 3			0
Transfers out of Level 3			0
Ending Balance	0	0	0
Asset- backed Securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Included in realized gains / losses	0	0
Included in other comprehensive income	0	0
Acquisitions	0	0
Sales	0	0
Amortization	0	0
Other	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Collateralized debt obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	50,364	63,505	71,598
Included in realized gains / losses			(6,787)
Included in other comprehensive income			12,447
Acquisitions			0
Sales			(13,213)
Amortization			4,505
Other			(5,045)
Transfers into Level 3			0
Transfers out of Level 3			0
Ending Balance	42,146	50,364	63,505
Collateralized debt obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Included in realized gains / losses	0	0
Included in other comprehensive income	(8,230)	(13,771)
Acquisitions	0	0
Sales	0	0
Amortization	4,569	4,519
Other	(4,557)	(3,889)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Corporates
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance	478,083	641,688	714,505
Included in realized gains / losses			3,275
Included in other comprehensive income			(20,818)
Acquisitions			25,000
Sales			0
Amortization			9
Other			(80,283)
Transfers into Level 3			0
Transfers out of Level 3			0
Ending Balance	454,733	478,083	$ 641,688
Corporates | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Included in realized gains / losses	0	0
Included in other comprehensive income	4,541	(91,385)
Acquisitions	0	0
Sales	0	0
Amortization	155	7
Other	(28,046)	(72,227)
Transfers into Level 3	0	0
Transfers out of Level 3	$ 0	$ 0