Investments (Unrealized Losses) (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,525,000	$ 11,312,000
Other than temporary impairments Losses, Investments, Portion Not Recognized in Earnings	0	0
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	44,983,000	227,132,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 198,000	$ 883,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	39	233
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 24,021,000	$ 33,891,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 153,000	$ 607,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	33	46
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 69,004,000	$ 261,023,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 351,000	$ 1,490,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	72	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	$ 57,128,000	$ 230,030,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 1,868,000	$ 8,770,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	39	191
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 10,304,000	$ 9,936,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 303,000	$ 976,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	12	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 67,432,000	$ 239,966,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,171,000	$ 9,746,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	51	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		$ 14,992,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		$ 66,000
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		$ 14,992,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 0	$ 66,000
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	$ 18,000
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	$ 94,000	$ 98,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 2,000	$ 2,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	4	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 94,000	$ 116,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,000	$ 2,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	4	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	$ 1,345,000	$ 3,747,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 1,000	$ 8,000
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	$ 1,345,000	$ 3,747,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 1,000	$ 8,000
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	$ 103,456,000	$ 475,919,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 2,067,000	$ 9,727,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	80	442
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 34,419,000	$ 43,925,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 458,000	$ 1,585,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	49	58
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 137,875,000	$ 519,844,000
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2,525,000	$ 11,312,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	129	500