Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Significant transfers between Levels 1, 2 and 3	$ 0	$ 0

Fair value assets between level 1 level 2 and level 3 transfers amount.

No definition available.

Name:	clsd_FairValueAssetsBetweenLevel1Level2AndLevel3TransfersAmount
Namespace Prefix:	clsd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant