Represents an additional interest rate charge to outstanding loan balances in event of a default.

No definition available.

Name:	insm_AdditionalInterestRateToOutstandingLoanBalances
Namespace Prefix:	insm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of the backend fee that accompanies borrowing money under the debt instrument.

+ References

No definition available.

+ Details

Name:	insm_LineOfCreditFacilityBackendFeePercent
Namespace Prefix:	insm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of facility fee paid by the company.

+ References

No definition available.

+ Details

Name:	insm_LineOfCreditFacilityFacilityFee
Namespace Prefix:	insm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of minimum cash liquidity requirement to be consolidated.

+ References

No definition available.

+ Details

Name:	insm_LineOfCreditFacilityMinimumCashLiquidityRequirement
Namespace Prefix:	insm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of facility fee paid by the company.

+ References

No definition available.

+ Details

Name:	insm_LineOfCreditFacilityPercentOfFacilityFeePaid
Namespace Prefix:	insm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the payment of the end of term charge.

+ References

No definition available.

+ Details

Name:	insm_PaymentOfEndOfTermCharge
Namespace Prefix:	insm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

+ 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

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the 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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum amount borrowed under the credit facility at any time during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

+ Details

Name:	us-gaap_RepaymentsOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=us-gaap_PrivatePlacementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_TypeOfArrangementAxis=insm_LicenseAgreementWithAstrazenecaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Narrative (Details) - USD ($)			1 Months Ended		12 Months Ended
Debt - Narrative (Details) - USD ($)	Feb. 28, 2018	Sep. 30, 2016	Oct. 31, 2016	Jan. 31, 2016	Dec. 31, 2017	Sep. 29, 2016	Jun. 29, 2012
Debt
Payment of end of term charge				$ 390,000
Hercules
Debt
Maximum borrowing capacity of term loan							$ 25,000,000
Interest rate (as a percent)							9.25%
A&R Loan Agreement
Debt
Maximum borrowing capacity of term loan		$ 55,000,000
Interest rate (as a percent)			9.25%
Amount outstanding		35,000,000				$ 25,000,000
Amount of borrowings during the period		$ 10,000,000	$ 20,000,000
Facility fee paid (as a percent)					0.375%
Backend fee (as a percent)			4.15%
Facility fee			$ 337,500
Minimum cash liquidity requirement eliminated					$ 25,000,000
Additional interest rate in event of default (as a percent)					5.00%
A&R Loan Agreement \| License Agreement with AstraZeneca
Debt
Amount outstanding			$ 20,000,000
A&R Loan Agreement \| Prime Rate
Debt
Basis spread (as a percent)			(4.50%)
Forecast \| A&R Loan Agreement
Debt
Prepayment of debt	$ 58,000,000