Employee Benefit Plans - Summary of Restricted Stock Units (Details) - Restricted Stock Units - $ / shares	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Number of Shares
Unvested at December 31, 2018	5,752,046
Granted	5,449,311
Vested	(2,859,765)
Forfeited	(1,147,189)
Unvested at September 30, 2019	7,194,403	5,752,046
Weighted Average Grant-Date Fair Value
Unvested at December 31, 2018	$ 12.77
Granted	15.01
Vested	12.93
Forfeited	13.42
Unvested at September 30, 2019	$ 14.30	$ 12.77
Weighted Average Remaining Contractual Term (in years)
Unvested, Weighted Average Remaining Contractual Term	2 years 2 months 12 days	1 year 2 months 12 days

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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