Equity and Equity Compensation Plans - Summary of Common Stock Reserved for Future Issuance: 2017 EIP (Details) - shares	Sep. 30, 2021	Dec. 31, 2020	Jul. 26, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options issued and outstanding options (in shares)	4,374,257	5,733,738
Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options issued and outstanding options (in shares)	4,374,257	5,733,738
Restricted stock units issued and outstanding or deferred (in shares)	3,452,462	4,459,743
Shares available for future equity grants (in shares)	16,718,941	11,309,377
Total shares reserved for future issuance (in shares)	24,545,660	21,502,858	7,898,159

Aggregate number of common shares reserved for future issuance.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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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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
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