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Fair Value Measurements - Quantitative Information used in Valuing Level 3 Liabilities (Details) - Discounted Cash Flow $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Contingent Payment Arrangements | Growth rates
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input	0.07	0.07
Contingent Payment Arrangements | Growth rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input	0.07	0.07
Contingent Payment Arrangements | Discount rates
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input	0.15	0.15
Contingent Payment Arrangements | Discount rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangements, measurement input	0.15	0.15
Affiliate Equity Repurchase Obligations | Growth rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	(0.04)	(0.04)
Affiliate Equity Repurchase Obligations | Growth rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.09	0.09
Affiliate Equity Repurchase Obligations | Growth rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.05	0.03
Affiliate Equity Repurchase Obligations | Discount rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.13	0.14
Affiliate Equity Repurchase Obligations | Discount rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.17	0.16
Affiliate Equity Repurchase Obligations | Discount rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Affiliate equity repurchase obligations, measurement input	0.15	0.15
Significant Unobservable Inputs (Level 3) | Contingent Payment Arrangements
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value liabilities	$ 2.0	$ 1.9
Significant Unobservable Inputs (Level 3) | Affiliate Equity Repurchase Obligations
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value liabilities	$ 75.4	$ 36.2

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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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