Earnings per Share - Dilutive and Antidilutive securities (Details) shares in Millions, item in Millions	6 Months Ended
Jun. 30, 2019 item shares	Jun. 30, 2018 item shares
Class A Units
Antidilutive securities and effect of dilutive securities
Potential shares of common stock contingently issuable upon conversion of the Class A units \| item	11.2	9.8
Restricted stock
Antidilutive securities and effect of dilutive securities
Number of anti-dilutive common shares excluded from the calculation of diluted income per share \| shares	12.8	11.9

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration