Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, available-for-sale, amortized cost	$ 7,441,048	$ 7,185,754
Fixed Income Securities, Available-for-sale, Allowance for Credit Loss	(33,554)	(45,721)	$ (37,599)	$ (9,724)
Unrealized gains	20,461	9,262
Unrealized losses	(463,439)	(537,188)
Debt Securities, Available-for-sale, Fair Value	6,964,516	6,612,107
U.S. Government and Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, available-for-sale, amortized cost	360,176	209,528
Fixed Income Securities, Available-for-sale, Allowance for Credit Loss	0	0
Unrealized gains	1,347	37
Unrealized losses	(18,153)	(20,326)
Debt Securities, Available-for-sale, Fair Value	343,370	189,239
Foreign Government [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, available-for-sale, amortized cost	11,185	11,199
Fixed Income Securities, Available-for-sale, Allowance for Credit Loss	(36)	(284)	(150)	(46)
Unrealized gains	0	0
Unrealized losses	(1,262)	(1,307)
Debt Securities, Available-for-sale, Fair Value	9,887	9,608
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, available-for-sale, amortized cost	713,515	965,231
Fixed Income Securities, Available-for-sale, Allowance for Credit Loss	(737)	(1,024)	(1,991)	(137)
Unrealized gains	3,048	1,812
Unrealized losses	(33,743)	(48,001)
Debt Securities, Available-for-sale, Fair Value	682,083	918,018
Corporate Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, available-for-sale, amortized cost	2,631,373	2,558,655
Fixed Income Securities, Available-for-sale, Allowance for Credit Loss	(16,756)	(30,330)	(23,066)	(6,682)
Unrealized gains	8,375	3,509
Unrealized losses	(175,042)	(196,809)
Debt Securities, Available-for-sale, Fair Value	2,447,950	2,335,025
Collateralized Loan Obligations and Other Asset Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, available-for-sale, amortized cost	1,631,305	1,607,660
Fixed Income Securities, Available-for-sale, Allowance for Credit Loss	(3,895)	(2,375)	(2,283)	(939)
Unrealized gains	4,765	2,408
Unrealized losses	(102,040)	(121,720)
Debt Securities, Available-for-sale, Fair Value	1,530,135	1,485,973
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, available-for-sale, amortized cost	1,396,241	1,169,546
Fixed Income Securities, Available-for-sale, Allowance for Credit Loss	(11,740)	(11,597)	(10,029)	(1,909)
Unrealized gains	2,543	1,148
Unrealized losses	(85,388)	(99,265)
Debt Securities, Available-for-sale, Fair Value	1,301,656	1,059,832
Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed income securities, available-for-sale, amortized cost	697,253	663,935
Fixed Income Securities, Available-for-sale, Allowance for Credit Loss	(390)	(111)	$ (80)	$ (11)
Unrealized gains	383	348
Unrealized losses	(47,811)	(49,760)
Debt Securities, Available-for-sale, Fair Value	$ 649,435	$ 614,412

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).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (i)
-URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: