Basis of Presentation - Additional Information (Detail) - Stamford Operating Lease [Member]	Mar. 31, 2019 Lease	Jan. 01, 2019 USD ($)
Basis Of Presentation [Line Items]
Annual incremental borrowing rate	7.00%
Operating lease, renewable term	5 years
ASC 842 [Member]
Basis Of Presentation [Line Items]
Number of operating lease \| Lease	1
Annual incremental borrowing rate	7.00%
Operating lease, renewable term	5 years
Cumulative effect adjustment \| $		$ 0

Basis of presentation.

No definition available.

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Namespace Prefix:	cara_
Data Type:	xbrli:stringItemType
Balance Type:	na
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- Definition

Number of operating lease.

+ References

No definition available.

+ Details

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Namespace Prefix:	cara_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

+ References

No definition available.

+ Details

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

- Definition

Discount rate used by lessee to determine present value of operating lease payments.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

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

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

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Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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