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Condensed Statements of Cash Flows (Parenthetical) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
10% Convertible promissory notes  
Conversion of convertible promissory notes into preferred stock, accrued interest $ 923us-gaap_InterestPayableCurrentAndNoncurrent
/ us-gaap_DebtConversionByUniqueDescriptionAxis
= us-gaap_ConvertibleNotesPayableMember
Pfizer note  
Conversion of convertible promissory notes into preferred stock, accrued interest $ 274us-gaap_InterestPayableCurrentAndNoncurrent
/ us-gaap_DebtConversionByUniqueDescriptionAxis
= espr_PfizerConvertibleNoteMember