Summary of Investments - Fair Value of Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fixed maturities:
Carrying Value	$ 1,781,865	$ 1,825,438
Fixed maturities
Fixed maturities:
Cost or Amortized Cost	1,697,219	1,720,291
Gross Unrealized Appreciation	90,962	107,003
Gross Unrealized Depreciation	6,146	1,851
Fair Value	1,782,035	1,825,443
Allowance for Credit Losses	170	5
Carrying Value	1,781,865	1,825,438
Short-Term Investments
Fixed maturities:
Cost or Amortized Cost	800	175
Gross Unrealized Appreciation	1
Gross Unrealized Depreciation	0
Fair Value	801
Allowance for Credit Losses	0
Carrying Value	801
Total Available-for-Sale Investments
Fixed maturities:
Cost or Amortized Cost	1,698,019
Gross Unrealized Appreciation	90,963
Gross Unrealized Depreciation	6,146
Fair Value	1,782,836
Allowance for Credit Losses	170
Carrying Value	1,782,666
U.S. Treasury
Fixed maturities:
Cost or Amortized Cost	73,072	149,481
Gross Unrealized Appreciation	318	482
Gross Unrealized Depreciation	420	25
Fair Value	72,970	149,938
Allowance for Credit Losses	0	0
Carrying Value	72,970	149,938
U.S. government agency
Fixed maturities:
Cost or Amortized Cost	79,070	60,502
Gross Unrealized Appreciation	3,073	4,016
Gross Unrealized Depreciation	1,071	0
Fair Value	81,072	64,518
Allowance for Credit Losses	0	0
Carrying Value	81,072	64,518
States, municipalities and political subdivisions \| General obligations \| Midwest
Fixed maturities:
Cost or Amortized Cost	70,118	77,933
Gross Unrealized Appreciation	3,155	4,047
Gross Unrealized Depreciation	0	0
Fair Value	73,273	81,980
Allowance for Credit Losses	0	0
Carrying Value	73,273	81,980
States, municipalities and political subdivisions \| General obligations \| Northeast
Fixed maturities:
Cost or Amortized Cost	28,964	29,071
Gross Unrealized Appreciation	1,010	1,379
Gross Unrealized Depreciation	0	0
Fair Value	29,974	30,450
Allowance for Credit Losses	0	0
Carrying Value	29,974	30,450
States, municipalities and political subdivisions \| General obligations \| South
Fixed maturities:
Cost or Amortized Cost	93,271	104,522
Gross Unrealized Appreciation	4,694	5,448
Gross Unrealized Depreciation	0	0
Fair Value	97,965	109,970
Allowance for Credit Losses	0	0
Carrying Value	97,965	109,970
States, municipalities and political subdivisions \| General obligations \| West
Fixed maturities:
Cost or Amortized Cost	97,282	102,590
Gross Unrealized Appreciation	6,334	7,431
Gross Unrealized Depreciation	0	0
Fair Value	103,616	110,021
Allowance for Credit Losses	0	0
Carrying Value	103,616	110,021
States, municipalities and political subdivisions \| Special revenue \| Midwest
Fixed maturities:
Cost or Amortized Cost	119,011	115,956
Gross Unrealized Appreciation	8,481	9,142
Gross Unrealized Depreciation	0	0
Fair Value	127,492	125,098
Allowance for Credit Losses	0	0
Carrying Value	127,492	125,098
States, municipalities and political subdivisions \| Special revenue \| Northeast
Fixed maturities:
Cost or Amortized Cost	56,067	56,317
Gross Unrealized Appreciation	4,392	4,759
Gross Unrealized Depreciation	0	0
Fair Value	60,459	61,076
Allowance for Credit Losses	0	0
Carrying Value	60,459	61,076
States, municipalities and political subdivisions \| Special revenue \| South
Fixed maturities:
Cost or Amortized Cost	202,317	208,739
Gross Unrealized Appreciation	16,266	17,967
Gross Unrealized Depreciation	49	0
Fair Value	218,534	226,706
Allowance for Credit Losses	0	0
Carrying Value	218,534	226,706
States, municipalities and political subdivisions \| Special revenue \| West
Fixed maturities:
Cost or Amortized Cost	130,229	129,417
Gross Unrealized Appreciation	9,225	9,982
Gross Unrealized Depreciation	0	0
Fair Value	139,454	139,399
Allowance for Credit Losses	0	0
Carrying Value	139,454	139,399
Foreign bonds
Fixed maturities:
Cost or Amortized Cost	26,359	27,799
Gross Unrealized Appreciation	1,199	1,805
Gross Unrealized Depreciation	73	2
Fair Value	27,485	29,602
Allowance for Credit Losses	0	0
Carrying Value	27,485	29,602
Public utilities
Fixed maturities:
Cost or Amortized Cost	95,984	76,114
Gross Unrealized Appreciation	5,907	7,388
Gross Unrealized Depreciation	88	0
Fair Value	101,803	83,502
Allowance for Credit Losses	0	0
Carrying Value	101,803	83,502
Corporate bonds \| Energy
Fixed maturities:
Cost or Amortized Cost	24,296	22,441
Gross Unrealized Appreciation	2,418	2,895
Gross Unrealized Depreciation	0	0
Fair Value	26,714	25,336
Allowance for Credit Losses	0	0
Carrying Value	26,714	25,336
Corporate bonds \| Industrials
Fixed maturities:
Cost or Amortized Cost	52,095	39,513
Gross Unrealized Appreciation	3,094	3,744
Gross Unrealized Depreciation	76	0
Fair Value	55,113	43,257
Allowance for Credit Losses	0	0
Carrying Value	55,113	43,257
Corporate bonds \| Consumer goods and services
Fixed maturities:
Cost or Amortized Cost	65,280	46,521
Gross Unrealized Appreciation	3,221	4,046
Gross Unrealized Depreciation	434	0
Fair Value	68,067	50,567
Allowance for Credit Losses	0	0
Carrying Value	68,067	50,567
Corporate bonds \| Health care
Fixed maturities:
Cost or Amortized Cost	28,984	6,678
Gross Unrealized Appreciation	704	898
Gross Unrealized Depreciation	302	0
Fair Value	29,386	7,576
Allowance for Credit Losses	0	0
Carrying Value	29,386	7,576
Corporate bonds \| Technology, media and telecommunications
Fixed maturities:
Cost or Amortized Cost	66,175	37,270
Gross Unrealized Appreciation	4,261	4,381
Gross Unrealized Depreciation	852	15
Fair Value	69,584	41,636
Allowance for Credit Losses	0	0
Carrying Value	69,584	41,636
Corporate bonds \| Financial services
Fixed maturities:
Cost or Amortized Cost	93,396	93,736
Gross Unrealized Appreciation	5,807	7,564
Gross Unrealized Depreciation	282	269
Fair Value	98,921	101,031
Allowance for Credit Losses	170	5
Carrying Value	98,751	101,026
Mortgage-backed securities
Fixed maturities:
Cost or Amortized Cost	24,800	20,305
Gross Unrealized Appreciation	268	326
Gross Unrealized Depreciation	162	54
Fair Value	24,906	20,577
Allowance for Credit Losses	0	0
Carrying Value	24,906	20,577
Collateralized mortgage obligations \| Government national mortgage association
Fixed maturities:
Cost or Amortized Cost	97,913	81,758
Gross Unrealized Appreciation	3,648	4,439
Gross Unrealized Depreciation	1,065	45
Fair Value	100,496	86,152
Allowance for Credit Losses	0	0
Carrying Value	100,496	86,152
Collateralized mortgage obligations \| Federal home loan mortgage corporation
Fixed maturities:
Cost or Amortized Cost	127,051	151,362
Gross Unrealized Appreciation	1,398	2,239
Gross Unrealized Depreciation	1,086	758
Fair Value	127,363	152,843
Allowance for Credit Losses	0	0
Carrying Value	127,363	152,843
Collateralized mortgage obligations \| Federal national mortgage association
Fixed maturities:
Cost or Amortized Cost	45,166	81,952
Gross Unrealized Appreciation	1,517	2,013
Gross Unrealized Depreciation	186	683
Fair Value	46,497	83,282
Allowance for Credit Losses	0	0
Carrying Value	46,497	83,282
Asset-backed securities
Fixed maturities:
Cost or Amortized Cost	319	314
Gross Unrealized Appreciation	572	612
Gross Unrealized Depreciation	0	0
Fair Value	891	926
Allowance for Credit Losses	0	0
Carrying Value	$ 891	$ 926

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
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Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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- Definition

Amount excluding accrued interest, 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/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
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