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

No definition available.

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Data Type:	xbrli:monetaryItemType
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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

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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

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Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Assets:
Total, Estimated Fair Value	$ 19,198		$ 26,419
Transfer of assets between levels	0	0
Recurring fair value measurement \| Level 1
Assets:
Money market fund	357		5,356
Total, Estimated Fair Value	11,702		16,782
Recurring fair value measurement \| Level 1 \| U.S. treasury notes
Assets:
Available for sale securities	11,108		11,188
Recurring fair value measurement \| Level 1 \| Certificates of deposit
Assets:
Available for sale securities	237		238
Recurring fair value measurement \| Level 2
Assets:
Total, Estimated Fair Value	7,496		9,637
Recurring fair value measurement \| Level 2 \| U.S. government agency securities
Assets:
Available for sale securities	7,496		9,637
Recurring fair value measurement \| Total
Assets:
Money market fund	357		5,356
Total, Estimated Fair Value	19,198		26,419
Recurring fair value measurement \| Total \| U.S. treasury notes
Assets:
Available for sale securities	11,108		11,188
Recurring fair value measurement \| Total \| U.S. government agency securities
Assets:
Available for sale securities	7,496		9,637
Recurring fair value measurement \| Total \| Certificates of deposit
Assets:
Available for sale securities	$ 237		$ 238