Fair value measurements - Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($)
Fair Value Disclosures [Abstract]
Beginning Balance at December 31, 2019	$ 1,856
Initial fair value of embedded derivatives issued	3,415
Change in fair value	1,581
Settlement	(6,852)
Ending Balance at December 31, 2020	$ 0

Embedded Derivative, Initial Fair Value of Embedded Derivatives Issued.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Embedded derivative liability Settlement.

+ References

No definition available.

+ Details

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Namespace Prefix:	bcab_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Net Increase or Decrease in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 15
-URI http://asc.fasb.org/subtopic&trid=2229187

+ Details

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Period Type:	duration

- References

No definition available.

+ Details

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