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Fair Value Measurements - Quantitative Information About Level 3 (Details) - Discounted cash flow $ in Millions	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Contingent payment arrangements | Growth rates
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangement, measurement input	0.07
Contingent payment arrangements | Growth rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangement, measurement input		0.07
Contingent payment arrangements | Growth rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangement, measurement input		0.08
Contingent payment arrangements | Growth rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangement, measurement input	0.07	0.07
Contingent payment arrangements | Discount rates
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangement, measurement input	0.15
Contingent payment arrangements | Discount rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangement, measurement input		0.15
Contingent payment arrangements | Discount rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangement, measurement input		0.16
Contingent payment arrangements | Discount rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Contingent payment arrangement, measurement input		0.15
Affiliate equity repurchase obligations | Growth rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Obligations to related parties, measurement input	(0.04)	0.00
Affiliate equity repurchase obligations | Growth rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Obligations to related parties, measurement input	0.09	0.11
Affiliate equity repurchase obligations | Growth rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Obligations to related parties, measurement input	0.03	0.06
Affiliate equity repurchase obligations | Discount rates | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Obligations to related parties, measurement input	0.14	0.12
Affiliate equity repurchase obligations | Discount rates | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Obligations to related parties, measurement input	0.16	0.16
Affiliate equity repurchase obligations | Discount rates | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Obligations to related parties, measurement input	0.15	0.14
Level 3 | Contingent payment arrangements
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value liabilities	$ 1.9	$ 9.4
Level 3 | Affiliate equity repurchase obligations
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value liabilities	$ 36.2	$ 49.2

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Fair value of financial and nonfinancial obligations.

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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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