Represent the amount related to increase (Decrease) in net cash provided by financing activities.

No definition available.

Name:	jrvr_IncreaseDecreaseInNetCashProvidedByFinancingActivities
Namespace Prefix:	jrvr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represent the amount related to increase (Decrease) in net cash provided by operating activities

+ References

No definition available.

+ Details

Name:	jrvr_IncreaseDecreaseInNetCashProvidedByOperatingActivities
Namespace Prefix:	jrvr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents number of insurance companies owned by the entity.

+ References

No definition available.

+ Details

Name:	jrvr_NumberOfInsuranceCompanies
Namespace Prefix:	jrvr_
Data Type:	xbrli:integerItemType
Balance Type:	na
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_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=64801991&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64801991&loc=d3e5747-111685

+ Details

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

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_NewAccountingPronouncementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Accounting Policies - Narrative (Details) $ in Millions	6 Months Ended
Accounting Policies - Narrative (Details) $ in Millions	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) company	Dec. 31, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in variable interest entities		$ 30.6	$ 27.1
Number of insurance companies based in the United States \| company		6
Accounting Standards Update ("ASU") 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in net cash provided by operating activities	$ 1.0
Increase in net cash provided by financing activities	$ 1.0