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Schedule I - Summary Of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost	$ 3,813,996
Investments	3,937,223	$ 5,740,791
Other Investments and Securities, at Cost	362,847
Other Investments	391,217	$ 431,630
U.S. Government Obligations [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities	94,394
Short-term Investments [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	430,405
Available-for-sale Securities	430,331
U S Government Obligations [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost	93,636
Fixed Income Securities [Member] | Municipal Bonds [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	882,631
Available-for-sale Securities	879,919
Fixed Income Securities [Member] | Corporate Debt Securities [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,288,882
Available-for-sale Securities	1,278,122
Fixed Income Securities [Member] | Debt Security, Government, Non-US [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	30,496
Available-for-sale Securities	30,834
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	221,825
Available-for-sale Securities	258,607
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	133,075
Available-for-sale Securities	131,356
Fixed Income Securities [Member] | Asset-backed Securities [Member]
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Available-for-sale Securities, Amortized Cost Basis	370,199
Available-for-sale Securities	$ 442,443

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Sum of the carrying amounts as of the balance sheet date of all investments.

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Includes other investments and securities that are not at fair value as of the balance sheet date and those that are not accounted for under the equity method.

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Cost of investment held by insurance company, excluding investment in related party.

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