Available for Sale Securities and Other Investments (Amortized Cost and Estimated Fair Value of Investments Classified as Available for Sale By Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
Due within one year, amortized cost	$ 1,608,076
Fixed maturities investments excluding mortgage-backed and asset-backed securities, amortized cost	1,608,076
Mortgage-backed and asset-backed securities, amortized cost	261,886
Debt securities, available for sale securities, amortized cost	1,869,962	$ 627,922
Estimated Fair Value
Due within one year, estimated fair value	1,607,725
Fixed maturities investments excluding mortgage-backed and asset-backed securities, estimated fair value	1,607,725
Mortgage-backed and asset-backed securities, estimated fair value	260,695
Debt securities, available for sale securities, estimated fair value	$ 1,868,420	$ 628,075

Fixed maturities investments excluding mortgage-backed and asset-backed securities, amortized cost.

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- Definition

Fixed maturities investments excluding mortgage-backed and asset-backed securities, estimated fair value.

+ References

No definition available.

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Mortgage backed and asset backed securities amortized cost.

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Mortgage Backed And Asset Backed Securities Estimated Fair Value

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- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amortized cost of investment in debt security measured at fair value with change recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), maturing in next fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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-Section 50
-Paragraph 3
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-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62586-112803

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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