Summary of Significant Accounting Policies - Additional Information (Detail) - ASU 2016-02 [Member]	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Increase in total assets on the consolidated balance sheet due to adoption of ASU 2016-02	$ 756,347
Increase in total liabilities on the consolidated balance sheet due to adoption of ASU 2016-02	$ 756,347

Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on liabilities.

No definition available.

Name:	alt_NewAccountingPronouncementOrChangeInAccountingPrincipleCumulativeEffectOfChangeOnLiabilities
Namespace Prefix:	alt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant