Fair Value Measurement Fair Value Inputs, Liabilities, Quantitative Information (Details)	6 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Adjusted EBITDA Volatility	25.00%	26.00%
WACC	8.25%	8.75%
20-year risk free rate	2.91%	2.58%
Market price of risk	5.20%	5.99%
Cost of debt	4.72%	4.08%

Fair Value Assumptions, Cost of Debt

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- Definition

Fair Value Assumptions, Expected Volatility Rate-Adjusted EBITDA

+ References

No definition available.

+ Details

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- Definition

Fair Value Assumptions, Market Price of Risk

+ References

No definition available.

+ Details

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- Definition

Risk-free interest rate assumption used in valuing an instrument.

+ 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 (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- References

No definition available.

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

+ Details

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