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Note 13 - Derivative Financial Instruments (Details) (USD $)
In Millions, unless otherwise specified
Jan. 31, 2011
Jul. 31, 2013
Sep. 30, 2013
May 31, 2013
Dec. 31, 2014
Jul. 31, 2014
Jul. 31, 2011
Note 13 - Derivative Financial Instruments (Details) [Line Items]              
Debt Instrument, Face Amount $ 40.0us-gaap_DebtInstrumentFaceAmount            
$40 Million Secured Debt Facility [Member] | Maximum [Member]              
Note 13 - Derivative Financial Instruments (Details) [Line Items]              
Performance Based Arranger Fee Percentage   18.00%bpz_PerformanceBasedArrangerFeePercentage
/ us-gaap_DebtInstrumentAxis
= bpz_FortyMillionDollarSecuredDebtFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		          
$40 Million Secured Debt Facility [Member]              
Note 13 - Derivative Financial Instruments (Details) [Line Items]              
Debt Instrument, Face Amount 40.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bpz_FortyMillionDollarSecuredDebtFacilityMember		   40.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bpz_FortyMillionDollarSecuredDebtFacilityMember		 25.5us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bpz_FortyMillionDollarSecuredDebtFacilityMember		      
$75 Million Secured Debt Facility [Member] | Maximum [Member]              
Note 13 - Derivative Financial Instruments (Details) [Line Items]              
Performance Based Arranger Fee Percentage         12.00%bpz_PerformanceBasedArrangerFeePercentage
/ us-gaap_DebtInstrumentAxis
= bpz_SeventyFiveMillionDollarSecuredDebtFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 12.00%bpz_PerformanceBasedArrangerFeePercentage
/ us-gaap_DebtInstrumentAxis
= bpz_SeventyFiveMillionDollarSecuredDebtFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
$75 Million Secured Debt Facility [Member]              
Note 13 - Derivative Financial Instruments (Details) [Line Items]              
Debt Instrument, Face Amount       $ 75.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bpz_SeventyFiveMillionDollarSecuredDebtFacilityMember		     $ 75.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= bpz_SeventyFiveMillionDollarSecuredDebtFacilityMember