Fair Value Measurements (Narrative) (Details)	6 Months Ended
Jun. 30, 2019 USD ($)
Fair Value Measurements [Abstract]
Transfers between levels	$ 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