Investments (Tables)

3 Months Ended

Mar. 31, 2024

Investments Debt And Equity Securities [Abstract]

Schedule of Disposition of Fixed Income and Equity Securities

Sales	Proceeds		Gross Realized				Net Realized
(in thousands)	From Sales		Gains		Losses		Gain (Loss)
2024
Fixed income securities - available-for-sale	$	11,819	$	289	$	(793)	$	(504)
Equity securities		15,910		7,234		(121)		7,113
2023
Fixed income securities - available-for-sale	$	3,790	$	35	$	(82)	$	(47)
Equity securities		3,501		2,417		(101)		2,316
Calls/Maturities			Gross Realized				Net Realized
(in thousands)	Proceeds		Gains		Losses		Gain (Loss)
2024
Fixed income securities - available-for-sale	$	72,423	$	33	$	(157)	$	(124)
2023
Fixed income securities - available-for-sale	$	190,305	$	35	$	(40)	$	(5)

Fair Value, Assets Measured on Recurring Basis

	As of March 31, 2024
	Quoted Prices in		Significant Other		Significant
	Active Markets for		Observable		Unobservable
	Identical Assets		Inputs		Inputs
(in thousands)	(Level 1)		(Level 2)		(Level 3)		Total
Fixed income securities - available-for-sale
U.S. government	$	—	$	329,559	$	—	$	329,559
U.S. agency		—		58,455		—		58,455
Non-U.S. government & agency		—		3,844		—		3,844
Agency MBS		—		414,428		—		414,428
ABS/CMBS/MBS*		—		289,476		—		289,476
Corporate		—		1,158,487		62,560		1,221,047
Municipal		—		546,512		—		546,512
Total fixed income securities - available-for-sale	$	—	$	2,800,761	$	62,560	$	2,863,321
Equity securities		641,758		—		1,609		643,367
Total	$	641,758	$	2,800,761	$	64,169	$	3,506,688

* Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities

	As of December 31, 2023
	Quoted Prices in		Significant Other		Significant
	Active Markets for		Observable		Unobservable
	Identical Assets		Inputs		Inputs
(in thousands)	(Level 1)		(Level 2)		(Level 3)		Total
Fixed income securities - available-for-sale
U.S. government	$	—	$	308,031	$	—	$	308,031
U.S. agency		—		59,826		—		59,826
Non-U.S. government & agency		—		3,882		—		3,882
Agency MBS		—		425,285		—		425,285
ABS/CMBS/MBS*		—		281,182		—		281,182
Corporate		—		1,164,548		60,471		1,225,019
Municipal		—		552,624		—		552,624
Total fixed income securities - available-for-sale	$	—	$	2,795,378	$	60,471	$	2,855,849
Equity securities		588,416		—		1,625		590,041
Total	$	588,416	$	2,795,378	$	62,096	$	3,445,890

* Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities

Summary of Changes in Balance of Level 3 Securities

(in thousands)	Level 3 Securities
Balance as of January 1, 2024	$	62,096
Net realized and unrealized gains (losses)
Included in other comprehensive earnings (loss)		(271)
Purchases		2,735
Sales / Calls / Maturities		(391)
Balance as of March 31, 2024	$	64,169
Change in unrealized gains (losses) during the period for Level 3 assets held at period-end - included in other comprehensive earnings (loss)	$	(271)

Schedule of Contractual Maturity of Securities

	March 31, 2024
(in thousands)	Amortized Cost		Fair Value
Due in one year or less	$	188,801	$	186,550
Due after one year through five years		875,943		843,536
Due after five years through 10 years		696,813		669,310
Due after 10 years		548,944		460,021
ABS/CMBS/MBS*		771,772		703,904
Total available-for-sale	$	3,082,273	$	2,863,321

* Asset-backed, commercial mortgage-backed and mortgage-backed securities

Schedule of Amortized Cost and Fair Value of Available-for-sale Securities

	March 31, 2024
	Cost or		Allowance		Gross		Gross
	Amortized		for Credit		Unrealized		Unrealized		Fair
(in thousands)	Cost		Losses		Gains		Losses		Value
U.S. government	$	337,014	$	—	$	388	$	(7,843)	$	329,559
U.S. agency		59,956		—		444		(1,945)		58,455
Non-U.S. government & agency		4,800		—		—		(956)		3,844
Agency MBS		456,358		—		1,208		(43,138)		414,428
ABS/CMBS/MBS*		315,414		(2)		970		(26,906)		289,476
Corporate		1,277,258		(235)		4,732		(60,708)		1,221,047
Municipal		631,473		—		1,413		(86,374)		546,512
Total Fixed Income	$	3,082,273	$	(237)	$	9,155	$	(227,870)	$	2,863,321
	December 31, 2023
	Cost or		Allowance		Gross		Gross
	Amortized		for Credit		Unrealized		Unrealized		Fair
(in thousands)	Cost		Losses		Gains		Losses		Value
U.S. government	$	312,632	$	—	$	1,257	$	(5,858)	$	308,031
U.S. agency		60,763		—		652		(1,589)		59,826
Non-U.S. government & agency		4,800		—		—		(918)		3,882
Agency MBS		460,551		—		2,636		(37,902)		425,285
ABS/CMBS/MBS*		308,458		(3)		611		(27,884)		281,182
Corporate		1,273,187		(303)		8,766		(56,631)		1,225,019
Municipal		634,000		—		2,238		(83,614)		552,624
Total Fixed Income	$	3,054,391	$	(306)	$	16,160	$	(214,396)	$	2,855,849

* Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities

Schedule of Debt Securities Available-for-sale Allowance for Credit Loss

	Three Months Ended March 31,
(in thousands)	2024		2023
Beginning balance	$	306	$	339
Increase to allowance from securities for which credit losses were not previously recorded		12		54
Reduction from securities sold during the period		(67)		—
Net increase (decrease) from securities that had an allowance at the beginning of the period		(14)		72
Balance as of March 31,	$	237	$	465

Schedule of Securities in an Unrealized Loss Position Segregated by Type and Length of Time in an Unrealized Loss Position

	March 31, 2024						December 31, 2023
(in thousands)	< 12 Mos.		12 Mos. & Greater		Total		< 12 Mos.		12 Mos. & Greater		Total
U.S. government
Fair value	$	78,413	$	203,962	$	282,375	$	37,718	$	204,556	$	242,274
Amortized cost		79,565		210,653		290,218		37,950		210,182		248,132
Unrealized loss	$	(1,152)	$	(6,691)	$	(7,843)	$	(232)	$	(5,626)	$	(5,858)
U.S. agency
Fair value	$	15,822	$	28,854	$	44,676	$	8,736	$	29,632	$	38,368
Amortized cost		15,995		30,626		46,621		8,790		31,167		39,957
Unrealized loss	$	(173)	$	(1,772)	$	(1,945)	$	(54)	$	(1,535)	$	(1,589)
Non-U.S. government
Fair value	$	—	$	3,844	$	3,844	$	—	$	3,882	$	3,882
Amortized cost		—		4,800		4,800		—		4,800		4,800
Unrealized Loss	$	—	$	(956)	$	(956)	$	—	$	(918)	$	(918)
Agency MBS
Fair value	$	55,007	$	288,704	$	343,711	$	61,196	$	275,707	$	336,903
Amortized cost		56,100		330,749		386,849		61,714		313,091		374,805
Unrealized loss	$	(1,093)	$	(42,045)	$	(43,138)	$	(518)	$	(37,384)	$	(37,902)
ABS/CMBS/MBS*
Fair value	$	25,663	$	182,583	$	208,246	$	12,240	$	211,436	$	223,676
Amortized cost		25,831		209,321		235,152		12,367		239,193		251,560
Unrealized loss	$	(168)	$	(26,738)	$	(26,906)	$	(127)	$	(27,757)	$	(27,884)
Corporate
Fair value	$	185,542	$	795,631	$	981,173	$	67,402	$	822,731	$	890,133
Amortized cost		188,580		853,301		1,041,881		68,345		878,419		946,764
Unrealized loss	$	(3,038)	$	(57,670)	$	(60,708)	$	(943)	$	(55,688)	$	(56,631)
Municipal
Fair value	$	74,207	$	418,819	$	493,026	$	61,218	$	391,361	$	452,579
Amortized cost		75,247		504,153		579,400		61,697		474,496		536,193
Unrealized loss	$	(1,040)	$	(85,334)	$	(86,374)	$	(479)	$	(83,135)	$	(83,614)
Total fixed income
Fair value	$	434,654	$	1,922,397	$	2,357,051	$	248,510	$	1,939,305	$	2,187,815
Amortized cost		441,318		2,143,603		2,584,921		250,863		2,151,348		2,402,211
Unrealized loss	$	(6,664)	$	(221,206)	$	(227,870)	$	(2,353)	$	(212,043)	$	(214,396)

* Non-agency asset-backed, commercial mortgage-backed and mortgage-backed securities

Schedule of Credit Quality Indicators for Investments in Unrealized Loss Positions

	Equivalent	Equivalent	(dollars in thousands)
NAIC	S&P	Moody’s	Amortized				Unrealized		Percent
Rating	Rating	Rating	Cost		Fair Value		Loss		to Total
1	AAA/AA/A	Aaa/Aa/A	$	2,137,898	$	1,941,077	$	(196,821)	86.4	%
2	BBB	Baa		397,220		369,097		(28,123)	12.3	%
3	BB	Ba		31,428		29,952		(1,476)	0.7	%
4	B	B		14,826		14,073		(753)	0.3	%
5	CCC	Caa		2,730		2,421		(309)	0.1	%
6	CC or lower	Ca or lower		819		431		(388)	0.2	%
		Total	$	2,584,921	$	2,357,051	$	(227,870)	100.0	%