Aggregate number of common shares reserved for future issuance.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Gross number of share options (or share units) granted during the period.

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No definition available.

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- Definition

Number of options outstanding, including both vested and non-vested options.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Stockholders' Equity - Equity Incentive Plans (Details) - USD ($) $ in Millions	12 Months Ended	40 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Mar. 22, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	41,400,000	41,400,000
Shares issued and outstanding (in shares)	1,300,000	1,300,000		5,000,000	5,400,000	13,400,000
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Options granted (in shares)		0
Remaining unamortized stock-based compensation	$ 429.0	$ 429.0
Unamortized stock-based compensation, requisite service period	2 years 9 months 18 days
2018 Plan \| Class A common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)			41,400,000
2018 Plan \| Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Vesting period	4 years
2008 Equity Incentive Plan, 2017 Equity Incentive Plan, and 2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued and outstanding (in shares)	26,300,000	26,300,000
Shares available for grant (in shares)	57,100,000	57,100,000