Investments Available-for-Sale Securities in a Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	$ 82,765	$ 222,581
Less than 12 months, gross unrealized holding losses	588	2,502
12 Months or Longer, Estimated Fair Value	110,212	128,301
12 Months or Longer, Gross Unrealized Holding Losses	2,344	4,366
Total Estimated Fair Value	192,977	350,882
Total Gross Unrealized Holding Losses	(2,932)	(6,868)
U.S. Treasury securities and obligations of U.S. government agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value		0
Less than 12 months, gross unrealized holding losses		0
12 Months or Longer, Estimated Fair Value		499
12 Months or Longer, Gross Unrealized Holding Losses		1
Total Estimated Fair Value		499
Total Gross Unrealized Holding Losses		(1)
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	0	42,718
Less than 12 months, gross unrealized holding losses	0	440
12 Months or Longer, Estimated Fair Value	9,756	34,326
12 Months or Longer, Gross Unrealized Holding Losses	54	854
Total Estimated Fair Value	9,756	77,044
Total Gross Unrealized Holding Losses	(54)	(1,294)
Corporate and other securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	2,313	62,045
Less than 12 months, gross unrealized holding losses	15	890
12 Months or Longer, Estimated Fair Value	12,143	12,092
12 Months or Longer, Gross Unrealized Holding Losses	295	511
Total Estimated Fair Value	14,456	74,137
Total Gross Unrealized Holding Losses	(310)	(1,401)
Commercial mortgage and asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	60,061	93,247
Less than 12 months, gross unrealized holding losses	532	1,017
12 Months or Longer, Estimated Fair Value	29,952	25,746
12 Months or Longer, Gross Unrealized Holding Losses	309	505
Total Estimated Fair Value	90,013	118,993
Total Gross Unrealized Holding Losses	(841)	(1,522)
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	20,391	24,571
Less than 12 months, gross unrealized holding losses	41	155
12 Months or Longer, Estimated Fair Value	58,361	55,638
12 Months or Longer, Gross Unrealized Holding Losses	1,686	2,495
Total Estimated Fair Value	78,752	80,209
Total Gross Unrealized Holding Losses	$ (1,727)	$ (2,650)