Balance Sheet Details (Composition of Property and Equipment) (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, plant and equipment, gross	$ 11,620,000	$ 11,143,000
Less: accumulated depreciation and amortization	(9,090,000)	(7,894,000)
Property and equipment, net	2,530,000	3,249,000
Furniture and Fixtures [Member]
Property, plant and equipment, gross	627,000	627,000
Leasehold Improvements [Member]
Property, plant and equipment, gross	$ 3,325,000	3,266,000
AmpliPhi Biosciences Corporation [Member]
Property, plant and equipment, gross		2,031,000	$ 1,986,000
Less: accumulated depreciation and amortization		(1,528,000)	(1,170,000)
Property and equipment, net		503,000	816,000
AmpliPhi Biosciences Corporation [Member] \| Laboratory Equipment [Member]
Property, plant and equipment, gross		1,771,000	1,727,000
AmpliPhi Biosciences Corporation [Member] \| Office and Computer Equipment [Member]
Property, plant and equipment, gross		72,000	71,000
AmpliPhi Biosciences Corporation [Member] \| Leasehold Improvements [Member]
Property, plant and equipment, gross		188,000	188,000
C3J [Member]
Property, plant and equipment, gross		11,143,000	10,784,000
Less: accumulated depreciation and amortization		(7,894,000)	(6,962,000)
Property and equipment, net		3,249,000	3,822,000
C3J [Member] \| Laboratory Equipment [Member]
Property, plant and equipment, gross		6,990,000	6,655,000
C3J [Member] \| Furniture and Fixtures [Member]
Property, plant and equipment, gross		627,000	627,000
C3J [Member] \| Office and Computer Equipment [Member]
Property, plant and equipment, gross		260,000	236,000
C3J [Member] \| Leasehold Improvements [Member]
Property, plant and equipment, gross		$ 3,266,000	$ 3,266,000

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.14)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.13)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ 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(14))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 3: 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)(8))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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(13))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LeaseholdImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=armp_AmpliphiBiosciencesCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=armp_LaboratoryEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=armp_OfficeAndComputerEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=armp_C3jTherapeuticsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: