Summary of Accounting Policies (Income Taxes Narrative) (Details)	12 Months Ended
Dec. 31, 2017
Accounting Policies [Abstract]
Valuation Allowance, Methodologies and Assumptions	A valuation allowance is provided when it is more likely than not (likelihood of greater than 50%) that some portion or all of the deferred tax assets will not be realized. Tax positions that meet the more-likely-than-not threshold are measured using a probability weighted approach as the largest amount of tax benefit that is greater than 50% likely of being realized upon settlement.

Describes the methodologies and assumptions on which the valuation allowance is based for deferred tax assets for which it is more likely than not that all or a portion of the deferred tax asset will not be realized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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