Securities In An Unrealized Loss Position Securities In An Unrealized Loss Position (Narrative) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2017 USD ($) shares	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	$ 4,550,212		$ 5,160,888
Gross Unrealized Losses	73,546		99,268
Available For Sale Equity Securities Gross Unrealized Gains	$ 404,192		453,298
Noninvestment Grade Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities \| shares	1
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	$ 23,600		22,034
Gross Unrealized Losses	2,106		3,639
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	0	$ 0
Available For Sale Equity Securities Gross Unrealized Gains	70,795		101,392
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	27,678		9,091
Gross Unrealized Losses	2,148		1,046
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	27,700
Available For Sale Equity Securities Gross Unrealized Gains	333,397		$ 351,906
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Equity Securities Gross Unrealized Gains	$ 2,100

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=73527792&loc=d3e27290-111563

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ 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=73527792&loc=d3e27290-111563

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

+ References

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=73527792&loc=d3e27161-111563

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