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Warrants - Warrants Outstanding (Detail)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Class of Warrant or Right [Line Items]    
Warrants outstanding 177us-gaap_ClassOfWarrantOrRightOutstanding 338us-gaap_ClassOfWarrantOrRightOutstanding
Warrants to Purchase Common Stock [Member]    
Class of Warrant or Right [Line Items]    
Warrants outstanding 177us-gaap_ClassOfWarrantOrRightOutstanding
/ us-gaap_ClassOfWarrantOrRightAxis
= blue_WarrantsToPurchaseCommonStockMember
338us-gaap_ClassOfWarrantOrRightOutstanding
/ us-gaap_ClassOfWarrantOrRightAxis
= blue_WarrantsToPurchaseCommonStockMember