Represents the final principal and interest payment due under the debt agreement.

No definition available.

Name:	exas_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestFinalPaymentDue
Namespace Prefix:	exas_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The total amount of long-term debt principal and interest payments to be paid through the maturity date of the debt agreement.

+ References

No definition available.

+ Details

Name:	exas_LongTermDebtMaturitiesRepaymentsOfPrincipalAndInterestThroughMaturityDate
Namespace Prefix:	exas_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the maximum funds available under the debt agreement.

+ References

No definition available.

+ Details

Name:	exas_MaximumFundAvailableUnderDebtAgreement
Namespace Prefix:	exas_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of amortization expense attributable to debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(8))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(8))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

Name:	us-gaap_AmortizationOfFinancingCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Amount, after accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=exas_DebtAgreementToFinanceBuildingPurchaseAndImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

LONG-TERM DEBT (Details) - USD ($) $ in Thousands	3 Months Ended
LONG-TERM DEBT (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2015
Long-term debt
Amortization of debt issuance costs	$ 402
Debt Agreement to Finance Building Purchase and Improvements
Long-term debt
Maximum funds available under debt agreement			$ 5,100
Interest rate (as a percent)			4.15%
Total amount of principal and interest payments to be paid through the maturity date of the debt agreement			$ 31
Final principal and interest payment due under the debt agreement			4,400
Deferred financing costs			$ 73
Amortization of debt issuance costs	$ 4	$ 4