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RELATED PARTY TRANSACTIONS - Additional Information (Details)	6 Months Ended
	Sep. 30, 2019
RELATED PARTY TRANSACTIONS
Percentage Of Annual Management Fee	0.50%

X

- Definition

The percentage of annual management fee.

+ References

No definition available.

+ Details

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Namespace Prefix:	bctciv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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