Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

No definition available.

+ Details

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

- Definition

Minimum amount of other commitment maturing in the next fiscal year following the latest fiscal year for commitments not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in this taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

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

- Definition

Amount of asset related to consideration paid in advance for other costs that provide economic benefits within a future period of one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6787-107765

+ Details

Name:	us-gaap_OtherPrepaidExpenseCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_ProductLiabilityContingencyLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

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

- Details

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

- Details

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

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Product Liability Contingency [Line Items]
Other Prepaid Expense, Current	$ 0.4	$ 0.3
Other Commitment, Due in Next Twelve Months	0.9
Drug Supplier Project Plan [Member]
Product Liability Contingency [Line Items]
Other Commitment	1.5
Manufacturer Of Prexigebersen [Member]
Product Liability Contingency [Line Items]
Other Commitment	1.0
Manufacture Of Drug Substance [Member]
Product Liability Contingency [Line Items]
Other Commitment	0.4
Manufacturing Development [Member]
Product Liability Contingency [Line Items]
Other Commitment	$ 0.1