Investment Operations Fixed Maturity and Equity Securities with Unrealized Losses by Length of Time (Details) $ in Thousands	Dec. 31, 2019 USD ($) issuers securities	Dec. 31, 2018 USD ($) issuers securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	189	709
Available For Sale Securities In Unrealized Loss Positions Qualitative Disclosure Number Of Issuers | issuers	145	465
Debt Securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 361,629	$ 1,923,500
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(6,075)	(82,010)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	205,139	603,763
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(16,283)	(46,931)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	566,768	2,527,263
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (22,358)	$ (128,941)
Percent of Total	100.00%	100.00%
Corporate
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 114,520	$ 1,035,176
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2,476)	(60,299)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	84,719	207,381
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(13,055)	(30,634)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	199,239	1,242,557
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (15,531)	$ (90,933)
Percent of Total	69.50%	70.50%
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 68,743	$ 191,365
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,435)	(4,482)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	6,941	74,113
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(494)	(2,760)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	75,684	265,478
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,929)	$ (7,242)
Percent of Total	8.60%	5.60%
Commercial mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 46,537	$ 302,159
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,266)	(9,947)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	2,610	148,855
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(147)	(9,443)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	49,147	451,014
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,413)	$ (19,390)
Percent of Total	6.30%	15.00%
Other asset-backed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 112,462	$ 250,119
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(519)	(3,397)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	102,439	149,997
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2,095)	(1,932)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	214,901	400,116
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (2,614)	$ (5,329)
Percent of Total	11.70%	4.10%
United States Government and agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	2,494	6,474
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(5)	(134)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,494	6,474
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (5)	$ (134)
Percent of Total	0.00%	0.10%
States and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 19,367	$ 144,681
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(379)	(3,885)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	5,936	16,943
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(487)	(2,028)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	25,303	161,624
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (866)	$ (5,913)
Percent of Total	3.90%	4.70%