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Organization and Business - Additional Information (Detail) (USD $)
 0 Months Ended 1 Months Ended 12 Months Ended
Jan. 15, 2014
Jan. 31, 2014
Dec. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2013
Nov. 05, 2013
Organization and Nature of Operations [Line Items]              
Cash     $ 13,858,798us-gaap_Cash $ 12,453,767us-gaap_Cash $ 16,819,783us-gaap_Cash $ 3,551,832us-gaap_Cash  
Authorized capital to be raised             100,000,000bpth_AuthorisedCapitalToBeRaised
Stock issued during period, shares, new issues 5,000,000us-gaap_StockIssuedDuringPeriodSharesNewIssues 5,000,000us-gaap_StockIssuedDuringPeriodSharesNewIssues          
Stock issued during period, value, new issues 15,000,000us-gaap_StockIssuedDuringPeriodValueNewIssues            
Proceeds from issuance initial public offering 13,800,000us-gaap_ProceedsFromIssuanceInitialPublicOffering            
Proceeds from Stock Options Exercised     $ 435,500us-gaap_ProceedsFromStockOptionsExercised        
Common Stock              
Organization and Nature of Operations [Line Items]              
Exercise of stock options (in shares)     525,000us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember		        
Warrant              
Organization and Nature of Operations [Line Items]              
Stock issued during period, shares, new issues 2,500,000us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_WarrantMember