Condensed Statement of Convertible Preferred Stock (Parenthetical) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Series B Convertible Preferred Stock
Issuance of convertible preferred stock for cash, issuance costs	$ 266

Amount of costs incurred with the issuance of temporary equity.

No definition available.

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