Investments (Fixed Maturities and Equity Securities Proceeds)(Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Proceeds from maturities/prepayments	$ 1,062,236	$ 1,371,000	$ 813,721
Fixed Maturities \| Available-for-sale Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Proceeds from sales	569,151	833,562	171,589
Proceeds from maturities/prepayments	492,944	495,969	642,503
Gross investment gains from sales and maturities	44,458	94,262	12,496
Gross investment losses from sales and maturities	(9,956)	(10,475)	(1,528)
OTTI recognized in earnings	(7,379)	(17,677)	(1,463)
Non-cash related proceeds	(100)	(1,500)	400
Equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Non-cash related proceeds	0		0
Equity securities \| Available-for-sale Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Proceeds from sales	510	34,618	5,732
Gross investment gains from sales and maturities	11	363	400
Gross investment losses from sales and maturities	0	(1,933)	0
OTTI recognized in earnings	$ (136)	$ 0	$ (3)

This item represents the gross profit realized on the sale of debt or equity securities 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 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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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 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=82896770&loc=SL6284422-111562

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The cash inflow associated with maturities (principal being due), prepayments and calls (requests of early payments) on securities not classified as either held-to-maturity securities or trading securities which are classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

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-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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