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Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2014
Series A preferred stock    
Payments of Stock Issuance Costs $ (120)us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesAPreferredStockMember		  
Series A-1 preferred stock    
Payments of Stock Issuance Costs 53us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_StatementClassOfStockAxis
= espr_SeriesA1PreferredStockMember		  
Common Stock.    
Payments of Stock Issuance Costs $ 2,671us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember		 $ 260us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember