Investments Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	$ 1,228,040	$ 1,161,862
Equity securities, Estimated Fair Value	177,637	148,011
Marketable Securities, Total	1,228,040	1,161,862
Level 1 Inputs
Fair value of financial instruments
Marketable Securities, Total	144,361	115,493
Level 1 Inputs \| Equity securities
Fair value of financial instruments
Equity securities, Estimated Fair Value	144,361	115,493
Level 2 Inputs
Fair value of financial instruments
Marketable Securities, Total	1,228,040	1,161,862
Level 2 Inputs \| U.S. Treasury securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	1,512	1,777
Level 2 Inputs \| Obligations of states and political subdivisions
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	251,396	266,198
Level 2 Inputs \| Residential mortgage-backed securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	307,202	297,023
Level 2 Inputs \| Commercial mortgage-backed securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	109,738	60,336
Level 2 Inputs \| Other asset-backed securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	36,222	61,076
Level 2 Inputs \| Corporate and other securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	521,970	475,452
Level 3 Inputs
Fair value of financial instruments
Marketable Securities, Total	516	680
Level 3 Inputs \| Equity securities
Fair value of financial instruments
Equity securities, Estimated Fair Value	516	680
Total
Fair value of financial instruments
Marketable Securities, Total	1,372,917	1,278,035
Total \| U.S. Treasury securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	1,512	1,777
Total \| Obligations of states and political subdivisions
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	251,396	266,198
Total \| Residential mortgage-backed securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	307,202	297,023
Total \| Commercial mortgage-backed securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	109,738	60,336
Total \| Other asset-backed securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	36,222	61,076
Total \| Corporate and other securities
Fair value of financial instruments
Fixed maturity securities, Estimated Fair Value	521,970	475,452
Total \| Equity securities
Fair value of financial instruments
Equity securities, Estimated Fair Value	$ 144,877	$ 116,173

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
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