Fair Value Measurement (Level 3 Assets) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	$ 22,819	$ 19,295	$ 17,820	$ 15,257
Included in earnings, as a part of:
Included in other comprehensive income	71	212	(140)	134
Purchases	4,841	5,995	11,889	11,055
Sales	(2,760)	(2,551)	(4,472)	(3,399)
Transfers in	10	0	908	0
Transfers out	(3,964)	(2,805)	(4,962)	(2,811)
Ending Balance	20,859	20,121	20,859	20,121
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Net investment Income [Member]
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(34)	(25)	(73)	(40)
Net realized investment gains (losses) [Member]
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(124)	0	(111)	(75)
Corporate debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	18,914	13,649	14,810	14,500
Included in earnings, as a part of:
Included in other comprehensive income	(70)	204	(278)	129
Purchases	4,841	5,995	11,889	5,995
Sales	(1,848)	(2,016)	(3,560)	(2,697)
Transfers in	10	0	10	0
Transfers out	(3,964)	0	(4,962)	(6)
Ending Balance	17,849	17,810	17,849	17,810
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Corporate debt [Member] \| Net investment Income [Member]
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(34)	(22)	(73)	(36)
Corporate debt [Member] \| Net realized investment gains (losses) [Member]
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0	13	(75)
Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	3,002	4,088	3,007	757
Included in earnings, as a part of:
Included in other comprehensive income	3	7	(2)	5
Purchases	0	0	0	3,500
Sales	0	(535)	0	(702)
Transfers in	0	0	0	0
Transfers out	0	(2,805)	0	(2,805)
Ending Balance	3,005	755	3,005	755
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Asset-backed securities [Member] \| Net investment Income [Member]
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0	0	0
Asset-backed securities [Member] \| Net realized investment gains (losses) [Member]
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0	0	0
All other investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	903	1,558	3	0
Included in earnings, as a part of:
Included in other comprehensive income	138	1	140	0
Purchases	0	0	0	1,560
Sales	(912)	0	(912)	0
Transfers in	0	0	898	0
Transfers out	0	0	0	0
Ending Balance	5	1,556	5	1,556
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
All other investments [Member] \| Net investment Income [Member]
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	(3)	0	(4)
All other investments [Member] \| Net realized investment gains (losses) [Member]
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	$ (124)	$ 0	$ (124)	$ 0

Included in Earnings, as a part of.

No definition available.

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Amount of unrealized (holding) gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
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- Definition

Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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