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Fair Value Measurements - Quantitative Information used in Valuing Level 3 Liabilities (Details) - Discounted Cash Flow $ in Millions	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Contingent Payment Arrangements | Growth rates
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input	0.07
Contingent Payment Arrangements | Growth rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input		0.07
Contingent Payment Arrangements | Growth rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input		0.08
Contingent Payment Arrangements | Discount rates
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input	0.15
Contingent Payment Arrangements | Discount rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input		0.15
Contingent Payment Arrangements | Discount rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input		0.16
Affiliate Equity Obligations | Growth rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.04	0.00
Affiliate Equity Obligations | Growth rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.09	0.11
Affiliate Equity Obligations | Discount rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.14	0.12
Affiliate Equity Obligations | Discount rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.16	0.16
Significant Unobservable Inputs (Level 3) | Contingent Payment Arrangements
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value liabilities	$ 4.3	$ 9.4
Significant Unobservable Inputs (Level 3) | Affiliate Equity Obligations
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value liabilities	$ 28.7	$ 49.2

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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