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

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Aggregate number of common shares reserved for future issuance.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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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 income (expense) related to nonoperating activities, classified as other.

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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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Number of shares authorized for issuance under share-based payment arrangement.

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

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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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Percentage of vesting of award under share-based payment arrangement.

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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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Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Details) - USD ($)			1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 26, 2018	Sep. 25, 2018	Aug. 31, 2019	Feb. 28, 2017	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Jan. 01, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock					10,674,126		10,674,126		8,331,103
Aggregate intrinsic value of stock options exercised					$ 300,000	$ 5,000	$ 2,200,000	$ 81,000
Weighted-average estimated grant-date fair value of employee stock options granted					$ 12.84	$ 5.60	$ 14.71	$ 5.03
Share-based compensation arrangement by share-based payment award options, shares granted							266,724		266,724
Stock-based compensation expense					$ 5,907,000	$ 3,011,000	$ 9,859,000	$ 5,718,000
Liability attributable to call option plan					$ 137,000		$ 137,000		$ 109,000
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common stock granted							1,511,750
Shares vesting period							4 years
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock		2,300,000
Annual increase period of common stock reserved for issuance		10 years
Maximum number of shares issuable										2,287,605
Shares available for grant					1,555,985		1,555,985
2018 Equity Incentive Plan \| Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested granted					$ 32,500,000	6,200,000	$ 32,500,000	$ 6,200,000
Remaining unrecognized compensation cost expected to be recognized over weighted-average period							3 years 6 months	2 years 9 months 18 days
2018 Equity Incentive Plan \| Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested granted					27,500,000	20,100,000	$ 27,500,000	$ 20,100,000
Remaining unrecognized compensation cost expected to be recognized over weighted-average period							2 years 7 months 6 days	2 years 7 months 6 days
2018 Equity Incentive Plan \| Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense					$ 100,000	100,000	$ 100,000	$ 100,000
2018 Equity Incentive Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in stock reserved for issuance as percentage of capital stock outstanding on last day of preceding year		5.00%
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock	230,000
Annual increase period of common stock reserved for issuance	10 years
Increase in stock reserved for issuance as percentage of capital stock outstanding on last day of preceding year	1.00%
Maximum number of shares issuable	2,300,000				725,714		725,714
Shares available for grant					421,277		421,277
Shares available for grant, increase										457,521
Call Option Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense					$ 26,000	64,000	$ 46,000	68,000
Other income (expense)					$ (12,000)	$ (1,800,000)	$ 18,000	$ (2,000,000.0)
Call Option Plan \| Option Granted in February 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award options, shares granted				248,944
Call options expiration period				1 year
Call Option Plan \| Option Granted in February 2017 \| January 1 , 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Call options vesting percentage				25.00%
Call Option Plan \| Option Granted in February 2017 \| January 1 , 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Call options vesting percentage				25.00%
Call Option Plan \| Option Granted in February 2017 \| January 1 , 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Call options vesting percentage				25.00%
Call Option Plan \| Option Granted in February 2017 \| January 1 , 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Call options vesting percentage				25.00%
Call Option Plan \| Option Granted in August 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award options, shares granted			17,780
Call options expiration period			1 year
Call Option Plan \| Option Granted in August 2019 \| January 1 , 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Call options vesting percentage			25.00%
Call Option Plan \| Option Granted in August 2019 \| January 1 , 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Call options vesting percentage			25.00%
Call Option Plan \| Option Granted in August 2019 \| January 1 , 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Call options vesting percentage			25.00%
Call Option Plan \| Option Granted in August 2019 \| January 1 , 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Call options vesting percentage			25.00%
Call Option Plan \| Vaxcyte, Inc.
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock					266,724		266,724