Fair Value - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
Jun. 29, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair value of level III, assets	$ 0	$ 0
Fair value of level III, liabilities	0	0
Transfers between levels I, II and III	$ 0	$ 0

Assets or liabilities transferred into or out of levels I, II or III during the reporting period.

No definition available.

Name:	ck0000815917_FairValueTransfersBetweenLevelsTransfersAmount
Namespace Prefix:	ck0000815917_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration