Investments (Unrealized Losses) (Details) $ in Thousands	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,982	$ 11,312
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	67,893	227,132
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 75	$ 883
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	60	233
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 51,053	$ 33,891
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 385	$ 607
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	70	46
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 118,946	$ 261,023
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 460	$ 1,490
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	130	279
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 53,090	$ 230,030
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 1,747	$ 8,770
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	42	191
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 19,818	$ 9,936
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 771	$ 976
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	24	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 72,908	$ 239,966
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,518	$ 9,746
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	66	199
Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 14,992
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		$ 66
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year		11
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 14,992
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 0	$ 66
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		11
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	$ 18
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	0	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 96	$ 98
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 3	$ 2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	5	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 96	$ 116
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 3	$ 2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	5	7
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 2,001	$ 3,747
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 1	$ 8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	2	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 2,001	$ 3,747
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 1	$ 8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	2	4
Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 122,984	$ 475,919
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 1,823	$ 9,727
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	104	442
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 70,967	$ 43,925
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 1,159	$ 1,585
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	99	58
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 193,951	$ 519,844
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,982	$ 11,312
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	203	500