Investments Available-for-Sale Securities in a Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	$ 301,127	$ 119,831
Less than 12 months, gross unrealized holding losses	7,827	458
12 Months or Longer, Estimated Fair Value	22,916	24,091
12 Months or Longer, Gross Unrealized Holding Losses	109	245
Total Estimated Fair Value	324,043	143,922
Total Gross Unrealized Holding Losses	7,936	703
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	38,432	6,412
Less than 12 months, gross unrealized holding losses	1,730	67
12 Months or Longer, Estimated Fair Value	0	0
12 Months or Longer, Gross Unrealized Holding Losses	0	0
Total Estimated Fair Value	38,432	6,412
Total Gross Unrealized Holding Losses	1,730	67
Corporate and other securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	114,920	3,829
Less than 12 months, gross unrealized holding losses	3,428	86
12 Months or Longer, Estimated Fair Value	0	0
12 Months or Longer, Gross Unrealized Holding Losses	0	0
Total Estimated Fair Value	114,920	3,829
Total Gross Unrealized Holding Losses	3,428	86
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	25,069	57,750
Less than 12 months, gross unrealized holding losses	16	149
12 Months or Longer, Estimated Fair Value	17,373	23,825
12 Months or Longer, Gross Unrealized Holding Losses	54	233
Total Estimated Fair Value	42,442	81,575
Total Gross Unrealized Holding Losses	70	382
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	9,556	4,971
Less than 12 months, gross unrealized holding losses	230	27
12 Months or Longer, Estimated Fair Value	0	0
12 Months or Longer, Gross Unrealized Holding Losses	0	0
Total Estimated Fair Value	9,556	4,971
Total Gross Unrealized Holding Losses	230	27
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	113,150	46,869
Less than 12 months, gross unrealized holding losses	2,423	129
12 Months or Longer, Estimated Fair Value	5,543	266
12 Months or Longer, Gross Unrealized Holding Losses	55	12
Total Estimated Fair Value	118,693	47,135
Total Gross Unrealized Holding Losses	$ 2,478	$ 141