Investments Available-for-Sale Securities in a Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	$ 1,068,989	$ 626,932
Less than 12 months, gross unrealized holding losses	57,212	9,015
12 Months or Longer, Estimated Fair Value	84,195	23,512
12 Months or Longer, Gross Unrealized Holding Losses	9,335	745
Total Estimated Fair Value	1,153,184	650,444
Total Gross Unrealized Holding Losses	66,547	9,760
U.S. Treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	13,984	6,847
Less than 12 months, gross unrealized holding losses	560	89
12 Months or Longer, Estimated Fair Value	0	0
12 Months or Longer, Gross Unrealized Holding Losses	0	0
Total Estimated Fair Value	13,984	6,847
Total Gross Unrealized Holding Losses	560	89
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	87,590	23,870
Less than 12 months, gross unrealized holding losses	6,590	469
12 Months or Longer, Estimated Fair Value	1,709	0
12 Months or Longer, Gross Unrealized Holding Losses	316	0
Total Estimated Fair Value	89,299	23,870
Total Gross Unrealized Holding Losses	6,906	469
Corporate and other securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	414,688	188,522
Less than 12 months, gross unrealized holding losses	28,493	3,718
12 Months or Longer, Estimated Fair Value	16,100	1,092
12 Months or Longer, Gross Unrealized Holding Losses	2,555	103
Total Estimated Fair Value	430,788	189,614
Total Gross Unrealized Holding Losses	31,048	3,821
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	207,664	136,669
Less than 12 months, gross unrealized holding losses	2,088	204
12 Months or Longer, Estimated Fair Value	5,788	4,452
12 Months or Longer, Gross Unrealized Holding Losses	95	48
Total Estimated Fair Value	213,452	141,121
Total Gross Unrealized Holding Losses	2,183	252
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	284,332	260,251
Less than 12 months, gross unrealized holding losses	17,784	4,329
12 Months or Longer, Estimated Fair Value	58,926	17,968
12 Months or Longer, Gross Unrealized Holding Losses	6,204	594
Total Estimated Fair Value	343,258	278,219
Total Gross Unrealized Holding Losses	23,988	4,923
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	60,731	10,773
Less than 12 months, gross unrealized holding losses	1,697	206
12 Months or Longer, Estimated Fair Value	1,672	0
12 Months or Longer, Gross Unrealized Holding Losses	165	0
Total Estimated Fair Value	62,403	10,773
Total Gross Unrealized Holding Losses	$ 1,862	$ 206