Deferred Revenues and Contract Liabilities - Additional Information (Detail) $ in Millions	6 Months Ended
Jun. 30, 2023 USD ($)
Accruals and deferred income including contract liabilities [abstract]
Increase in deferred revenues and contract liabilities	$ 0.2

Adjustments for increase decrease in deferred revenues and contract liabilities.

No definition available.

Name:	clls_AdjustmentsForIncreaseDecreaseInDeferredRevenuesAndContractLiabilities
Namespace Prefix:	clls_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration