REVENUE - Deferred Revenue Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Revenue from Contract with Customer, Liability [Roll Forward]
Beginning balance	$ 54,792	$ 26,307
Amount from beginning balance recognized into revenue	(54,792)	(26,307)
Recognition of deferred revenue	(139,371)	(91,193)
Deferral of revenue	237,638	145,985
Ending balance	$ 98,267	$ 54,792

Contract With Customer, Liability, Additions During the Period

No definition available.

Name:	duol_ContractWithCustomerLiabilityAdditionsDuringThePeriod
Namespace Prefix:	duol_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Contract with Customer, Liability, Revenue Recognized, Excluding Opening Balance

+ References

No definition available.

+ Details

Name:	duol_ContractWithCustomerLiabilityRevenueRecognizedExcludingOpeningBalance
Namespace Prefix:	duol_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Revenue from Contract with Customer, Liability

+ References

No definition available.

+ Details

Name:	duol_RevenueFromContractWithCustomerLiabilityRollForward
Namespace Prefix:	duol_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=123360276&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123360276&loc=SL49130532-203044

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130549-203045

+ Details

Name:	us-gaap_ContractWithCustomerLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130549-203045

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration