Significant Subsidiaries (Details Textual)	3 Months Ended
Jun. 30, 2012
Equity Method Investment, Ownership Percentage Criteria	Local Limited Partnership invested in by the Fund represents more than 20% of the Fund's total assets or equity as of June 30, 2012 or 2011 or net losses for the three months then ended.

Description about the percentage criteria of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

No definition available.

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Namespace Prefix:	bftcviii_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration