Securities In An Unrealized Loss Position Non-Investment Grade Fixed Maturity Securities (Details) $ in Thousands	9 Months Ended
Sep. 30, 2016 USD ($) shares position	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	$ 2,556,639	$ 4,170,376
Available For Sale Equity Securities Gross Unrealized Gains	6,788	8,216
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	45,198	113,948
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	2,459,431	4,121,586
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	33,729	91,406
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	70,980	22,320
Available For Sale Equity Securities Gross Unrealized Gains	6,573	8,216
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	9,028	3,353
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	26,000
Aggregate fair value of securities in a continuous unrealized loss position	26,228	26,470
Available For Sale Equity Securities Gross Unrealized Gains	215	0
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	2,441	19,189
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	357,896	566,793
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	5,775	11,308
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	1,133,419	1,281,545
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	12,074	14,414
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	355,297	608,633
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	2,585	6,269
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	83,075	188,718
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	2,490	12,689
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	436,102	1,309,737
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	$ 9,874	$ 44,393
Noninvestment Grade Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities \| shares	3
Noninvestment Grade Investments at Loss Less than 5 Million [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	31
Aggregate fair value of securities in a continuous unrealized loss position	$ 89,878
Gross Unrealized Loss	$ 5,805
Noninvestment Grade Investments at Loss Less than 5 Million [Member] \| Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	11
Aggregate fair value of securities in a continuous unrealized loss position	$ 23,921
Gross Unrealized Loss	$ 1,229
Noninvestment Grade Investments at Loss Less than 5 Million [Member] \| Foreign Government Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	4
Aggregate fair value of securities in a continuous unrealized loss position	$ 23,001
Gross Unrealized Loss	$ 1,101
Noninvestment Grade Investments at Loss Less than 5 Million [Member] \| Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	10
Aggregate fair value of securities in a continuous unrealized loss position	$ 27,531
Gross Unrealized Loss	3,045
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Equity Securities Gross Unrealized Gains	$ 2,000
Noninvestment Grade Investments at Loss Less than 5 Million [Member] \| Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities \| position	5
Aggregate fair value of securities in a continuous unrealized loss position	$ 8,418
Gross Unrealized Loss	$ 405

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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