FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Percentage of construciton completion threshold percentage when most entrepreneurial profit is earned	40.00%
Investment Owned, Unrecognized Unrealized Appreciation (Depreciation), Net	$ 28.7	$ 26.3
Thirteen Properties [Member] \| Minimum [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Percentage of completion of construction	40.00%

Percentage of Completion of construction during the reporting period.

No definition available.

Name:	jcap_PercentageOfCompletionOfConstruction
Namespace Prefix:	jcap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Company estimate of entrepreneurial profit is earned during construction period at construction threshold percentage.

+ References

No definition available.

+ Details

Name:	jcap_PercentageOfCompletionThresholdRelatedToConstruction
Namespace Prefix:	jcap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueConcentrationOfRiskFinancialStatementCaptionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the net excess or deficiency of the fair value of an investment (security, contract) over or under its cost (face amount, notional amount), respectively, which excess value or deficiency has not been recognized in earnings of the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=50485924&loc=SL6090603-123010

+ Details

Name:	us-gaap_InvestmentOwnedUnrecognizedUnrealizedAppreciationDepreciationNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=jcap_ThirteenPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: