Essentialis, Inc. Acquisition - Pro Forma Information (Details) - Essentialis, Inc. [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Business Acquisition [Line Items]
Pro forma total revenue	$ 376	$ 390	$ 641	$ 837
Pro forma net loss	$ (4,422)	$ (4,150)	$ (8,202)	$ (7,964)
Pro forma net loss per share - basic and diluted (in usd per share)	$ (0.08)	$ (0.12)	$ (0.12)	$ (0.18)
Proforma weighted-average shares - basic and diluted (in shares)	53,855,669	35,070,296	69,363,153	44,496,176

Business Acquisition, Pro Forma Earnings Per Share, Basic and Diluted

No definition available.

Name:	capn_BusinessAcquisitionProFormaEarningsPerShareBasicandDiluted
Namespace Prefix:	capn_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Pro Forma Weighted Average Shares Outstanding, Basic and Diluted

+ References

No definition available.

+ Details

Name:	capn_ProFormaWeightedAverageSharesOutstandingBasicandDiluted
Namespace Prefix:	capn_
Data Type:	xbrli:sharesItemType
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_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463

+ Details

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

- Definition

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=capn_EssentialisInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: