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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended			12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Depreciation expense				$ 17.4	$ 16.4	$ 12.6
Investment yields before tax assumed in premium deficiency assessment	2.40%	2.50%	3.00%
Deferred policy acquisition costs amortized to expense				$ 450.3	$ 399.4	$ 364.3

X

- Definition

This element represents the investment yields assumed in the premium deficiency assessment, which are based on the entity's actual average investment yield before tax as of the calculation date.

+ References

No definition available.

+ Details

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- Definition

Amount of expense related to deferred policy acquisition costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(7)(a))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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-Name Accounting Standards Codification
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- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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