Agreement Metric, Capital Distribution Percentage

No definition available.

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

- Definition

Agreement Metric, Capital Distribution Percentage to Third Party

+ References

No definition available.

+ Details

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

- Definition

Agreement Metric, Internal Rate of Return

+ References

No definition available.

+ Details

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

- Definition

Agreement Metric, Return Multiple

+ References

No definition available.

+ Details

Name:	jcap_AgreementMetricReturnMultiple
Namespace Prefix:	jcap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

It represents the investment yield percentage on purchase price that the entity has to pay if it exercises the put option.

+ References

No definition available.

+ Details

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

- Definition

Joint venture agreement percentage of priority distribution percentage of commited principal amount.

+ References

No definition available.

+ Details

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

- Definition

Total number of investments held by the company.

+ References

No definition available.

+ Details

Name:	jcap_NumberOfInvestment
Namespace Prefix:	jcap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of assets reported by an equity method investment of the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721683-107760

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33912-111571

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Definition

The amount of liabilities reported by an equity method investment of the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33912-111571

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721683-107760

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

Name:	us-gaap_EquityMethodInvestmentSummarizedFinancialInformationLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of net income (loss) reported by an equity method investment of the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721683-107760

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33912-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

For investments which are quantified by principal amount, the principle balance held at close of period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 6
-Subparagraph (SX 210.12-14.Column B)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12.Column B)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=63488139&loc=d3e12121-115841

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-12C.Column B)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010

+ Details

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

- Definition

Fair value portion of investments in an entity not consolidated. Includes, but is not limited to, investments in an entity that is affiliated with the reporting entity by means of direct or indirect ownership, an entity in which the reporting entity shares control of the entity with another party or group, an entity which the company has significant influence, but does not have control and subsidiaries that are not required to be consolidated and are accounted for using the equity or cost method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258

+ Details

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

- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes loans held for sale. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of other expense (income) that is infrequent in occurrence or unusual in nature.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64828382&loc=d3e15138-107781

+ Details

Name:	us-gaap_OtherNonrecurringIncomeExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow associated with the investment in or advances to an entity in which the reporting entity shares control of the entity with another party or group.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireInterestInJointVenture
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow from the sale of real estate held-for-investment and real estate joint ventures.

+ References

No definition available.

+ Details

Name:	us-gaap_ProceedsFromRealEstateAndRealEstateJointVentures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The book value of investments in real estate joint ventures including direct and indirect investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(d))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

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

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jcap_Sl1VentureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_ConsolidatedEntitiesAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jcap_IrrThresholdOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jcap_IrrThresholdTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jcap_IrrThresholdThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=jcap_HeitmanAndLargeInstitutionalCoinvestorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=jcap_HvpIiiStorageLendersInvestorLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

INVESTMENT IN SELF-STORAGE REAL ESTATE VENTURE (Narrative) (Details) $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($) property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 20, 2018 USD ($)	Aug. 09, 2017 USD ($)	Mar. 31, 2016 USD ($)
Investments Real Estate Properties [Line Items]
Investment in and advances to self-storage real estate venture	$ 14,846	$ 14,846		$ 13,856
Commitment amount	673,090	673,090		523,821
Funded principal	365,479	365,479		213,069		$ 24,754	$ 9,139
SL1 Venture [Member]
Investments Real Estate Properties [Line Items]
Investment in and advances to self-storage real estate venture	$ 2,000	$ 2,000		3,200
Equity method investment, ownership percentage	10.00%	10.00%
Development property investment, assets	$ 126,000	$ 126,000
Transaction and other expenses	200
Development property investment, liabilities	2,100	2,100
Development property investment, operating income (loss)	4,000	$ 9,100
Investment yield percentage on purchase price		4.50%
Commitment amount	123,300	$ 123,300
Joint venture agreement percentage of priority distribution percentage of commited principal amount		1.00%
Number of investments \| property			8
Funded principal	12,200	$ 12,200
Return of capital from real estate venture					$ 7,300
Agreement metric, return multiple		1.48
SL1 Venture [Member] \| Maximum [Member]
Investments Real Estate Properties [Line Items]
Commitment amount	12,300	$ 12,300
SL1 Venture [Member] \| Parent Company [Member]
Investments Real Estate Properties [Line Items]
Investment owned, aggregate committed principal amount								$ 41,900
Investments in joint venture, fair value								7,700
Development property investment, operating income (loss)	400	$ 1,000
Commitment amount			$ 12,300					8,100
Funded principal								$ 8,100
IRR Threshold One [Member]
Investments Real Estate Properties [Line Items]
Agreement metric, internal rate of return		14.00%
Agreement metric, capital distribution percentage to third party			10.00%
Agreement metric, capital distribution percentage		10.00%
IRR Threshold Two [Member]
Investments Real Estate Properties [Line Items]
Agreement metric, internal rate of return		17.00%
Agreement metric, capital distribution percentage to third party		20.00%
Agreement metric, capital distribution percentage		20.00%
IRR Threshold Three [Member]
Investments Real Estate Properties [Line Items]
Agreement metric, internal rate of return		20.00%
Agreement metric, capital distribution percentage to third party		30.00%
Agreement metric, capital distribution percentage		30.00%
Heitman And Large Institutional Co-Investor [Member] \| SL1 Venture [Member]
Investments Real Estate Properties [Line Items]
Investment in and advances to self-storage real estate venture	$ 110,000	$ 110,000
Equity method investment, ownership percentage	90.00%	90.00%
Transaction and other expenses		$ 2,000		3,200
HVP III Storage Lenders Investor, LLC [Member]
Investments Real Estate Properties [Line Items]
Payments to acquire interest in joint venture					$ 7,300
HVP III Storage Lenders Investor, LLC [Member] \| SL1 Venture [Member]
Investments Real Estate Properties [Line Items]
Development property investment, operating income (loss)	$ 3,600	8,100
Commitment amount	111,000	111,000
Development Property Investments [Member]
Investments Real Estate Properties [Line Items]
Commitment amount	583,784	583,784		$ 517,839
Eight Properties [Member] \| SL1 Venture [Member]
Investments Real Estate Properties [Line Items]
Commitment amount	$ 81,400	$ 81,400