Represents the transfer of assets between the levels of fair value hierarchy that have taken place during the period.

No definition available.

Name:	espr_FairValueMeasurementAssetTransfersBetweenLevels
Namespace Prefix:	espr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the transfer of liabilities between the levels of fair value hierarchy that have taken place during the period.

+ References

No definition available.

+ Details

Name:	espr_FairValueMeasurementLiabilityTransfersBetweenLevels
Namespace Prefix:	espr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Sum of investments and unrestricted cash measured at fair value as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	espr_InvestmentsAndCashFairValueDisclosure
Namespace Prefix:	espr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Total of debt securities categorized neither as held-to-maturity nor trading which are intended be sold or mature more than one year from the balance sheet date or operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

Name:	us-gaap_MoneyMarketFundsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USTreasuryNotesSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value Measurements (Details) (USD $)	12 Months Ended
Fair Value Measurements (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets:
Total, Estimated Fair Value	$ 56,901,000	$ 26,419,000
Transfer of assets between levels	0	0
Transfer of liabilities between levels		0	0
U.S. treasury notes
Assets:
Available for sale securities		11,188,000
U.S. government agency securities
Assets:
Available for sale securities		9,637,000
Certificates of deposit
Assets:
Available for sale securities		238,000
Level 1 \| U.S. treasury notes
Assets:
Available for sale securities		11,188,000
Level 1 \| Certificates of deposit
Assets:
Available for sale securities		238,000
Level 2
Assets:
Total, Estimated Fair Value		9,637,000
Level 2 \| U.S. government agency securities
Assets:
Available for sale securities		9,637,000
Recurring fair value measurement \| Level 1
Assets:
Money market fund	357,000	5,356,000
Total, Estimated Fair Value	16,652,000	16,782,000
Recurring fair value measurement \| Level 1 \| U.S. treasury notes
Assets:
Available for sale securities	11,513,000
Recurring fair value measurement \| Level 1 \| Certificates of deposit
Assets:
Available for sale securities	4,782,000
Recurring fair value measurement \| Level 2
Assets:
Total, Estimated Fair Value	40,249,000
Recurring fair value measurement \| Level 2 \| U.S. government agency securities
Assets:
Available for sale securities	40,249,000
Recurring fair value measurement \| Total
Assets:
Money market fund	357,000	5,356,000
Total, Estimated Fair Value	56,901,000	26,419,000
Recurring fair value measurement \| Total \| U.S. treasury notes
Assets:
Available for sale securities	11,513,000
Recurring fair value measurement \| Total \| U.S. government agency securities
Assets:
Available for sale securities	40,249,000
Recurring fair value measurement \| Total \| Certificates of deposit
Assets:
Available for sale securities	$ 4,782,000