ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Clinical hold-back, long-term (Details) $ in Thousands	6 Months Ended
Jun. 30, 2023 USD ($)
Agreements
Clinical holdback, Balance as of beginning of period	$ 464
Clinical holdback retained	158
Clinical holdback, Balance as of end of period	$ 622
Minimum
Agreements
Clinical holdback, Invoiced costs withheld from payment (as a percent)	5.00%
Maximum
Agreements
Clinical holdback, Invoiced costs withheld from payment (as a percent)	10.00%

Amount of liabilities representing agreed upon percentage of total invoiced costs withheld from payment by entity until the end of the study under the terms of agreement.

No definition available.

+ Details

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

- Definition

Percentage of total agreed upon invoiced costs withheld from payment by entity until the end of the study under the terms of agreement.

+ References

No definition available.

+ Details

Name:	aplt_ClinicalHoldbackPercentageOfTotalInvoicedCostsHeldBack
Namespace Prefix:	aplt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount retained during the period of liabilities representing agreed upon percentage of total invoiced costs withheld from payment by entity until the end of the study under the terms of agreement.

+ References

No definition available.

+ Details

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

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 808
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479402/808-10-50-1

+ Details

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

- Details

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

- Details

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