Common stock issued subject to repurchase related to early exercise of options.

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Employee stock purchase plans purchase price per share percentage.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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The number of shares converted in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Amount of cost to be recognized for option under share-based payment arrangement.

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Amount of cash outflow to satisfy grantee's tax withholding obligation for award under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

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

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- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Sep. 06, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized								380,000,000
Stock issuable upon the exercise of options outstanding			28,332,126		28,332,126		36,384,767
Proceeds from exercise of stock options					$ 12,354	$ 7,306
Share-based payment arrangement, expense			$ 20,716	$ 4,677	49,610	$ 10,016
Amounts withheld on behalf of employees for a future purchase					977
Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total compensation cost related to unvested awards not yet recognized			$ 67,800		$ 67,800		$ 90,500
Weighted average period over compensation cost related to unvested employee awards					2 years 2 months 12 days		2 years 8 months 12 days
Weighted average grant-date fair value of options granted					$ 16.55	$ 8.68
Proceeds from exercise of stock options					$ 12,400	$ 7,300
Intrinsic value of options exercised					443,400	106,000
Aggregate fair value of options vested					$ 19,600	$ 8,500
Early exercise of common stock			639,000		639,000		1,239,750
RSU
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average period over compensation cost related to unvested employee awards					3 years 6 months		3 years 10 months 24 days
Common stock granted					4,102,243
Total compensation cost related to unvested awards not yet recognized			$ 227,200		$ 227,200		$ 30,400
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of purchase the shares at a price per share		85.00%
Share-based payment arrangement, expense			$ 1,400		3,500
Amounts withheld on behalf of employees for a future purchase					$ 5,900
Class B Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, number of shares converted			16,808,933		134,419,844
Common stock, shares authorized			310,000,000		310,000,000		310,000,000
Common stock, par value			$ 0.00001		$ 0.00001		$ 0.00001
Common stock, shares issued			98,337,015		98,337,015		232,078,452
Common stock, shares outstanding			98,337,015		98,337,015		232,078,452
Stock issuable upon the exercise of options outstanding			28,296,826		28,296,826		36,364,067
Class A Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized			2,000,000,000		2,000,000,000		2,000,000,000
Common stock, par value			$ 0.00001		$ 0.00001		$ 0.00001
Common stock, shares issued			206,054,826		206,054,826		64,308,498
Common stock, shares outstanding			206,054,826		206,054,826		64,308,498
Stock issuable upon the exercise of options outstanding			35,300		35,300		20,700
Class A Common Stock \| Service-based Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock granted	96,210
Service based vesting period	4 years
Class A Common Stock \| 2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant			43,324,876		43,324,876
Class A Common Stock \| Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant			9,354,222		9,354,222
Issuance of common stock under the employee stock purchase plan					320,104