Cash flow leverage ratio.

No definition available.

Name:	basi_CashFlowLeverageRatio
Namespace Prefix:	basi_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of installments in which the debt instrument is to be repaid.

+ References

No definition available.

+ Details

Name:	basi_DebtInstrumentNumberOfRepaymentInstallments
Namespace Prefix:	basi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio of debt serve ratio one.

+ References

No definition available.

+ Details

Name:	basi_MinimumDebtServiceCoverageRatioOne
Namespace Prefix:	basi_
Data Type:	xbrli:pureItemType
Balance Type:	na
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

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120398452&loc=d3e534808-122878

+ Details

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

- Definition

Decrease for amounts of indebtedness forgiven by the holder of the debt instrument.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- 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

Amount of the required periodic payments including both interest and principal payments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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

- Definition

This item represents the amount that could be realized under a life insurance contract or contracts owned by the Entity as of the date of the statement of financial position. Such Entity-owned life insurance policies are commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 325
-SubTopic 30
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6384206&loc=d3e41899-111602

+ Details

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

- 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

Amount of the required periodic payments of both interest and principal.

+ References

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120398452&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120391452&loc=d3e13212-122682

+ Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=basi_PresidentAndChiefExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=basi_FirstInternetBankOfIndianaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=basi_EquipmentDrawLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=basi_ConstructionDrawLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=basi_SmithersAvanzaToxicologyServicesLlcAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=basi_PcrsAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=basi_CapitalExpenditureLineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=basi_HuntingtonNationalBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

DEBT - Additional Information (Details) $ in Thousands								6 Months Ended
DEBT - Additional Information (Details) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021 USD ($)	Jan. 31, 2021 USD ($)	Aug. 01, 2020 USD ($)	Apr. 23, 2020 USD ($) item	Mar. 27, 2020 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)
DEBT ARRANGEMENTS
Long-term Debt			$ 26,478					$ 26,478	$ 25,052
Minimum \| President and Chief Executive Officer [Member]
DEBT ARRANGEMENTS
Life Insurance, Corporate or Bank Owned, Amount			$ 5,000					$ 5,000
Credit Arrangements [Member] \| Maximum
DEBT ARRANGEMENTS
Minimum Debt Service Coverage Ratio One	1.20	1.10	1.05
Cash Flow Leverage Ratio	4.25	5.00	5.75					5.75
Credit Arrangements [Member] \| Minimum
DEBT ARRANGEMENTS
Minimum Debt Service Coverage Ratio One	1.00	1.00	1.0
Cash Flow Leverage Ratio	1.00	1.00	1.00					1.00
First Internet Bank of Indiana
DEBT ARRANGEMENTS
Debt Instrument, Periodic Payment								$ 33
Debt Instrument, Interest Rate, Stated Percentage			3.99%					3.99%
Debt Instrument, Face Amount			$ 4,500					$ 4,500
Long-term Debt, Gross			3,622					3,622
First Internet Bank of Indiana \| Equipment loan
DEBT ARRANGEMENTS
Long-term Debt			1,103					1,103
Line of Credit Facility, Additional Borrowing Capacity			$ 1,429					$ 1,429
First Internet Bank of Indiana \| Construction Draw Loan [Member]
DEBT ARRANGEMENTS
Debt Instrument, Interest Rate, Stated Percentage			5.20%					5.20%
Long-term Debt			$ 4,015					$ 4,015
Line of Credit Facility, Additional Borrowing Capacity			$ 4,445					$ 4,445
First Internet Bank of Indiana \| Revolving Facility
DEBT ARRANGEMENTS
Debt Instrument, Interest Rate, Stated Percentage			4.00%					4.00%
Line of Credit Facility, Additional Borrowing Capacity			$ 5,000					$ 5,000
Basis points deducted from prime rate								0.00%
Seller Note - Smithers Avanza \| Unsecured promissory note
DEBT ARRANGEMENTS
Debt Instrument, Interest Rate, Stated Percentage			6.50%					6.50%
Debt Instrument, Face Amount			$ 810					$ 810
Long-term Debt			$ 480					480
Paycheck protection program loan \| Unsecured promissory note
DEBT ARRANGEMENTS
Debt Instrument, Periodic Payment								$ 800
Debt Instrument, Interest Rate, Stated Percentage			4.50%					4.50%
Long-term Debt			$ 719					$ 719
Initial term loan [Member]
DEBT ARRANGEMENTS
Long-term Debt			$ 3,622					3,622	3,748
Subsequent Term Loan [Member] \| First Internet Bank of Indiana
DEBT ARRANGEMENTS
Debt Instrument, Periodic Payment								$ 78
Debt Instrument, Interest Rate, Stated Percentage			5.06%					5.06%
Debt Instrument, Face Amount			$ 5,500					$ 5,500
Long-term Debt			3,634					3,634
Third term loan
DEBT ARRANGEMENTS
Long-term Debt			$ 1,018					1,018	1,115
Third term loan \| First Internet Bank of Indiana
DEBT ARRANGEMENTS
Debt Instrument, Periodic Payment								$ 20
Debt Instrument, Interest Rate, Stated Percentage			4.63%					4.63%
Debt Instrument, Face Amount			$ 1,271					$ 1,271
Long-term Debt			1,018					1,018
Fifth term loan
DEBT ARRANGEMENTS
Long-term Debt			$ 1,858					$ 1,858	1,891
Fifth term loan \| First Internet Bank of Indiana
DEBT ARRANGEMENTS
Debt Instrument, Interest Rate, Stated Percentage			4.00%					4.00%
Debt Instrument, Face Amount			$ 1,939					$ 1,939
Long-term Debt			1,858					1,858
Fourth term loan
DEBT ARRANGEMENTS
Long-term Debt			$ 1,286					$ 1,286	1,425
Fourth term loan \| First Internet Bank of Indiana
DEBT ARRANGEMENTS
Debt Instrument, Interest Rate, Stated Percentage			4.00%					4.00%
Debt Instrument, Face Amount			$ 1,500					$ 1,500
Long-term Debt			1,286					1,286
Capex Line [Member] \| First Internet Bank of Indiana \| Capital Expenditure Line of Credit [Member]
DEBT ARRANGEMENTS
Debt Instrument, Face Amount			1,100					1,100
Long-term Debt			826				$ 948	$ 826
Basis points deducted from prime rate								4.00%
Line of Credit Facility, Periodic Payment					$ 17
Second Capex Line
DEBT ARRANGEMENTS
Long-term Debt			2,865					$ 2,865	$ 0
Second Capex Line \| First Internet Bank of Indiana \| Capital Expenditure Line of Credit [Member]
DEBT ARRANGEMENTS
Debt Instrument, Face Amount			3,000					3,000
Long-term Debt			$ 2,865					$ 2,865
Basis points deducted from prime rate								4.25%
Line of Credit Facility, Periodic Payment				$ 55
Payroll Protection Payroll (PPP) Program Loan
DEBT ARRANGEMENTS
Forgiveness of the loan							$ 4,851
Payroll Protection Payroll (PPP) Program Loan \| Huntington National Bank
DEBT ARRANGEMENTS
Debt Instrument, Periodic Payment						$ 283
Debt Instrument, Face Amount						$ 5,051
Number of installments for repayment \| item						18
Forgiveness of the loan						$ 4,851