Investments (Narrative) (Details) $ in Thousands	Sep. 30, 2017 USD ($) securities	Dec. 31, 2016 USD ($) securities
Schedule of Investments [Line Items]
Available-for-sale securities in unrealized loss position, number of positions \| securities	465	654
Available-for-sale securities, estimated fair value	$ 2,326,799	$ 3,790,614
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (51,838)	$ (99,981)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end \| securities	105	109
Available-for-sale securities, estimated fair value, 12 months or longer	$ 348,527	$ 321,552
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(12,773)	(17,204)
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	2,154,527	3,111,566
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (36,946)	$ (86,225)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end \| securities	90	93
Available-for-sale securities, estimated fair value, 12 months or longer	$ 336,316	$ 253,929
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	(8,844)	(8,636)
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	96,443	174,837
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses	$ (14,878)	$ (13,750)
Number of available-for-sale securities positions in a continuous unrealized loss position for one year or longer at period end \| securities	15	16
Available-for-sale securities, estimated fair value, 12 months or longer	$ 12,211	$ 67,623
Available-for-sale securities, gross unrealized holding and other-than-temporary impairment losses, 12 months or longer	$ (3,929)	$ (8,568)

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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