Name:	aplt_AccruedExpensesAndOtherCurrentLiabilities
Namespace Prefix:	aplt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of consideration transferred under the agreement during the period.

No definition available.

Name:	aplt_NonCollaborativeArrangementConsideration
Namespace Prefix:	aplt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of first payment to be made for license issue fee under non-collaborative arrangement.

No definition available.

Name:	aplt_NonCollaborativeArrangementLicenseIssueFeePaymentOne
Namespace Prefix:	aplt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of second payment to be made for license issue fee, due on first anniversary of the date of license, under non-collaborative arrangement.

No definition available.

Name:	aplt_NonCollaborativeArrangementLicenseIssueFeePaymentTwo
Namespace Prefix:	aplt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the payment on achievement of late stage regulatory milestones under non-collaborative arrangement.

No definition available.

Name:	aplt_NonCollaborativeArrangementPaymentOnAchievementOfLateStageRegulatoryMilestones
Namespace Prefix:	aplt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the payment to be made on achievement of specified patenting and development milestones under non-collaborative arrangement.

No definition available.

Name:	aplt_NonCollaborativeArrangementPaymentOnAchievementOfSpecifiedPatentingAndDevelopmentMilestones
Namespace Prefix:	aplt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the written notice period of material breach after which contract may be terminated if action to cure the breach is not initiated, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	aplt_NonCollaborativeCollaborativeArrangementCureOfMaterialBreachNotInitiatedTermination
Namespace Prefix:	aplt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the agreement term under non-collaborative arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	aplt_NonCollaborativeCollaborativeArrangementTerm
Namespace Prefix:	aplt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the written notice period for termination of agreement under non-collaborative arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	aplt_NonCollaborativeCollaborativeArrangementWrittenNoticePeriodForTerminationOfAgreement
Namespace Prefix:	aplt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The amount the entity will be required to pay of non-royalty sublicensing revenue received from third parties as a percent of non-royalty sublicensing revenue.

No definition available.

Name:	aplt_NonRoyaltySublicensingRevenuePercentage
Namespace Prefix:	aplt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

The royalties the entity will be required to pay as a percentage of on the Company's, the Company's affiliates' and the Company's sublicensees' net sales of licensed products.

No definition available.

Name:	aplt_RoyaltiesPercentage
Namespace Prefix:	aplt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

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.

No definition available.

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

The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.4)
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

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

Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

No definition available.

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

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 912
-SubTopic 730
-Section 25
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6472174&loc=d3e58812-109433

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

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

Name:	us-gaap_TypeOfArrangementAxis=aplt_LicenseAgreement2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_CounterpartyNameAxis=aplt_UniversityOfMiamiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

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