Basis of Presentation and Summary of Significant Accounting Policies - Reclassifications (Details) - Revenue - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Other revenue
Disaggregation of Revenue [Line Items]
Prior period reclassification adjustment	$ 4.0	$ 3.3
Marketplace revenue
Disaggregation of Revenue [Line Items]
Prior period reclassification adjustment	$ (4.0)	$ (3.3)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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