Schedule I - Summary Of Investments Other -Than-Investments In Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	$ 8,870,837	$ 9,470,795
Cost or Amortized Cost	10,738,238
Fixed maturity securities, fair value	9,572,145	10,215,328
Fair Value	11,489,915
Amount at which shown in balance sheet	11,479,076
Fixed maturity securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	8,870,837	9,470,795
Fixed maturity securities, fair value	9,572,145	$ 10,215,328
Amount at which shown in balance sheet	9,572,145
U.S. government and government agencies and authorities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	172,782
Fixed maturity securities, fair value	174,886
Amount at which shown in balance sheet	174,886
State, municipalities and political subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	446,882
Fixed maturity securities, fair value	476,075
Amount at which shown in balance sheet	476,075
Foreign governments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	508,871
Fixed maturity securities, fair value	568,468
Amount at which shown in balance sheet	568,468
Asset-backed
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	2,658
Fixed maturity securities, fair value	3,677
Amount at which shown in balance sheet	3,677
Commercial mortgage-backed
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	39,267
Fixed maturity securities, fair value	38,416
Amount at which shown in balance sheet	38,416
Residential mortgage-backed
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	1,071,179
Fixed maturity securities, fair value	1,101,312
Amount at which shown in balance sheet	1,101,312
U.S. corporate
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	5,022,769
Fixed maturity securities, fair value	5,461,250
Amount at which shown in balance sheet	5,461,250
Foreign corporate
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Fixed maturity securities available for sale, amortized cost	1,606,429
Fixed maturity securities, fair value	1,748,061
Amount at which shown in balance sheet	1,748,061
Equity securities:
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	381,831
Fair Value	421,361
Amount at which shown in balance sheet	421,361
Common stocks
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	11,911
Fair Value	20,794
Amount at which shown in balance sheet	20,794
Non-redeemable preferred stocks
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	369,920
Fair Value	400,567
Amount at which shown in balance sheet	400,567
Commercial mortgage loans on real estate
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	624,033
Fair Value	634,872
Amount at which shown in balance sheet	624,033
Policy loans
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	38,533
Fair Value	38,533
Amount at which shown in balance sheet	38,533
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	227,740
Fair Value	227,740
Amount at which shown in balance sheet	227,740
Other investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	595,264
Fair Value	595,264
Amount at which shown in balance sheet	$ 595,264