Investments - OTTI in Earnings on AFS Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI recognized in earnings	$ 1,553	$ 3,420	$ 6,893
Investments in fixed-maturity securities not in default [Member] \| Fixed-maturity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI recognized in earnings	1,001	3,257	5,108
Investments in fixed-maturity securities in default [Member] \| Fixed-maturity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI recognized in earnings	267	121	29
Equity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI recognized in earnings	$ 285	$ 42	$ 1,756

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.

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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration