Fair Value Measurements (Narrative) (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020
Fair Value Measurements [Abstract]
Transfers between levels	$ 0	$ 0

Amount of transfer of financial instrument between levels of the fair value hierarchy.

No definition available.

Name:	jcs_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisTransfersNet
Namespace Prefix:	jcs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration