Investments - Fair Value of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
AVAILABLE-FOR-SALE
Amortized Cost	$ 1,961,531	$ 1,771,041
Gross Unrealized Gain	3,640	6,810
Gross Unrealized Loss	96,840	91,348
Allowance for Credit Losses	0	1
Fair Value	1,868,331	1,686,503
US Treasury and government agencies
AVAILABLE-FOR-SALE
Amortized Cost	126,402	153,751
Gross Unrealized Gain	153	580
Gross Unrealized Loss	9,255	8,977
Allowance for Credit Losses	0	0
Fair Value	117,301	145,354
Foreign government
AVAILABLE-FOR-SALE
Amortized Cost		0
Gross Unrealized Gain		0
Gross Unrealized Loss		0
Allowance for Credit Losses		0
Fair Value		0
States, municipalities and political subdivisions
AVAILABLE-FOR-SALE
Amortized Cost	252,936	618,686
Gross Unrealized Gain	52	1,033
Gross Unrealized Loss	5,084	4,960
Allowance for Credit Losses	0	0
Fair Value	247,904	614,759
Corporate
AVAILABLE-FOR-SALE
Amortized Cost	728,662	671,618
Gross Unrealized Gain	1,354	3,327
Gross Unrealized Loss	40,633	44,413
Allowance for Credit Losses	0	1
Fair Value	689,382	630,532
Residential mortgage-backed
AVAILABLE-FOR-SALE
Amortized Cost	623,431	323,592
Gross Unrealized Gain	864	1,346
Gross Unrealized Loss	40,884	32,911
Allowance for Credit Losses	0	0
Fair Value	583,411	292,027
Commercial mortgage-backed
AVAILABLE-FOR-SALE
Amortized Cost	102,975	0
Gross Unrealized Gain	624	0
Gross Unrealized Loss	44	0
Allowance for Credit Losses	0	0
Fair Value	103,554	0
Other asset-backed
AVAILABLE-FOR-SALE
Amortized Cost	127,125	3,394
Gross Unrealized Gain	593	524
Gross Unrealized Loss	940	87
Allowance for Credit Losses	0	0
Fair Value	126,779	3,831
Asset-backed securities
AVAILABLE-FOR-SALE
Amortized Cost	853,531	326,986
Gross Unrealized Gain	2,081	1,870
Gross Unrealized Loss	41,868	32,998
Allowance for Credit Losses	0	0
Fair Value	$ 813,744	$ 295,858

Debt Securities, Available-for-Sale, Excluding Accrued Interest, Before Allowance For Credit Loss

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- Definition

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

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Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

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+ References

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