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Equity-Based Compensation - Narrative (Details) - USD ($)				1 Months Ended		9 Months Ended
	May 14, 2021	Jan. 01, 2021	Jan. 01, 2020	May 31, 2021	Sep. 30, 2017	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted in period (in shares)						4,427,586
Options outstanding (in shares)						11,059,955		7,227,296
Compensation cost not yet recognized						$ 7,820,000
Compensation expense recognition period						3 years
Weighted-average grant date fair value (in dollars per share)						$ 1.30	$ 1.33
Aggregate intrinsic value, stock options, exercised						$ 243,000	$ 74,000
Chief Financial Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted in period (in shares)				600,000
Options outstanding (in shares)						600,000
Exicure, Inc. 2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized, potential maximum additional shares (in shares)						4,600,000
Number of additional shares authorized, percentage of common stock outstanding						5.00%
Number of shares available for grant (in shares)						2,558,218
Options to purchase common stock | Exicure, Inc. 2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares available for grant (in shares)		4,382,567
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares available for grant (in shares)		258,207	262,954
Number of shares available for grant (in shares)						1,100,791
Maximum ESPP contribution rate as a percentage of compensation					15.00%
Maximum number of shares per employee in purchase period (in shares)					7,500
Maximum contribution amount					$ 25,000
ESPP purchase price as a percentage of market price					85.00%
Offering period duration					6 months
Issuance of common stock-ESPP (in shares)	103,096
Number of additional shares allowable annually under the plan (in shares)					300,000
Percentage of outstanding shares allowable as annual increase					0.30%
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares issued for each vested restricted stock unit (in shares)						1
Vesting period						4 years

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

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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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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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