Commitments - Other Commitment (Details) $ in Thousands	3 Months Ended
Sep. 30, 2018 USD ($)	Mar. 31, 2017 USD ($) item employee
Commitments
Proceeds from sale of outstanding loan	$ 5,600
Revolving loans
Commitments
Amount of potential loans offered		$ 15,000
Interest rate		2.00%
Expiration period		7 years
Members in the board of the entity \| item		5
Lannett employees as members of the board of the entity \| employee		1
Percentage of outstanding loan	50.00%
Proceeds from sale of outstanding loan	$ 5,600
Current amount due from outstanding loan	$ 5,800
Revolving loans \| If loan balance is equal to or greater than $7.5 million
Commitments
Minimum amount to be considered for conversion of loan to ownership interest		$ 7,500
Ownership interest for conversion (in percentage)		50.00%

Minimum amount to be considered for conversion of loan to ownership interest.

No definition available.

Name:	lci_MinimumAmountToBeConsideredForConversionOfLoanToOwnershipInterest
Namespace Prefix:	lci_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of employees of the company who are the members in the board of the entity.

+ References

No definition available.

+ Details

Name:	lci_NumberOfEmployeesInMembersOfBoardOfEntity
Namespace Prefix:	lci_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of members comprised in the board of the entity.

+ References

No definition available.

+ Details

Name:	lci_NumberOfMembersInBoardOfEntity
Namespace Prefix:	lci_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Ownership interest for conversion under agreement advances receivable, contractual obligations.

+ References

No definition available.

+ Details

Name:	lci_OwnershipInterestForConversionUnderAgreement
Namespace Prefix:	lci_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of outstanding loan sold to third party.

+ References

No definition available.

+ Details

Name:	lci_PercentageOfOutstandingLoanSoldToThirdParty
Namespace Prefix:	lci_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from the sale of outstanding loan to third party.

+ References

No definition available.

+ Details

Name:	lci_ProceedsFromSaleOfOutstandingLoanToThirdParty
Namespace Prefix:	lci_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The expiration period of agreement with VIE.

+ References

No definition available.

+ Details

Name:	lci_VariableInterestEntityExpirationPeriod
Namespace Prefix:	lci_
Data Type:	xbrli:durationItemType
Balance Type:	na
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

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

- Definition

Receivables to be collected from (obligations owed to) related parties, net as of the balance sheet date within one year where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Definition

The amount of financial or other support the reporting entity has provided (explicitly or implicitly) to the Variable Interest Entity (VIE) that it was not previously contractually required to provide or that the reporting entity intends to provide, including, for example, situations in which the reporting entity assisted the VIE in obtaining another type of support.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=77990344&loc=SL6759159-111685

+ Details

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

- Details

Name:	us-gaap_OtherCommitmentsAxis=lci_RevolvingLoanCommitmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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