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Stockholders' Equity - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
 0 Months Ended 1 Months Ended
Jan. 15, 2014
Jan. 31, 2014
Mar. 31, 2015
Dec. 31, 2014
Shareholders Equity [Line Items]        
Common stock and warrants issued, shares 5,000,000us-gaap_StockIssuedDuringPeriodSharesNewIssues 5,000,000us-gaap_StockIssuedDuringPeriodSharesNewIssues    
Common stock repurchased, shares   2,500,000bpth_CommonStockRepurchasedShares    
Common stock and warrants issued, Value   $ 15.0bpth_IssuanceOfCommonStockAndWarrantsValue    
Common Stock, shares issued     89,762,872us-gaap_CommonStockSharesIssued 89,762,872us-gaap_CommonStockSharesIssued
Common Stock, shares outstanding     89,762,872us-gaap_CommonStockSharesOutstanding 89,762,872us-gaap_CommonStockSharesOutstanding
Class of Warrant or Right, Exercise Price of Warrants or Rights   $ 4.74us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1    
Warrant        
Shareholders Equity [Line Items]        
Common stock and warrants issued, shares 2,500,000us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_WarrantMember		      
Class of Warrant or Right, Exercise Price of Warrants or Rights     0.90us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_WarrantMember