Changes In Equity And Comprehensive Income Line Items [Line Items]

No definition available.

Name:	alt_ChangesInEquityAndComprehensiveIncomeLineItemsLineItems
Namespace Prefix:	alt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Class of warrant or right exercise price of warrants or rights 2.

+ References

No definition available.

+ Details

Name:	alt_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights2
Namespace Prefix:	alt_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Class of warrant or right expiration period.

+ References

No definition available.

+ Details

Name:	alt_ClassOfWarrantOrRightExpirationPeriod
Namespace Prefix:	alt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Deemed dividend.

+ References

No definition available.

+ Details

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

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(4))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(2))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Face amount or stated value per share of common stock.

+ References

+ Details

Name:	us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

+ References

+ Details

Name:	us-gaap_CommonStockSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

+ Details

Name:	us-gaap_CommonStockSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

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(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of common units issued of limited liability company (LLC).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

+ Details

Name:	us-gaap_CommonUnitIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of common units of ownership outstanding of a limited liability company (LLC).

+ References

No definition available.

+ Details

Name:	us-gaap_CommonUnitOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Expense related to distribution, servicing and underwriting fees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.14)
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

+ Details

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

- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

+ Details

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

- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Date the subsidiary or equity investee issued or sold stock, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockTransactionDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share or per unit amount of equity securities issued.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesIssuedPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of new stock issued during the period.

+ 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(29))
-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 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=alt_FirstRegisteredDirectOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=alt_UnitOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=alt_CommonUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=alt_PrefundedUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=alt_SecondRegisteredDirectOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=alt_ThirdRegisteredDirectOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Common Stock - Additional Information (Detail) - USD ($)					12 Months Ended
	Mar. 12, 2019	Oct. 10, 2018	Oct. 02, 2018	Sep. 26, 2018	Dec. 31, 2018	Sep. 13, 2018	Sep. 12, 2018	Dec. 31, 2017	Mar. 31, 2017	Mar. 09, 2017
Changes In Equity And Comprehensive Income Line Items [Line Items]
Common stock, shares authorized					200,000,000	200,000,000	100,000,000	100,000,000
Common stock, par or stated value per share					$ 0.0001	$ 0.0001		$ 0.0001
Common stock, shares issued					9,078,735			609,280
Common stock, shares outstanding					9,078,238			608,499
Net proceeds from offering					$ 4,334,816
Per share exercise price					$ 5.03					$ 0.01
Shares of common stock called by warrants										1,659
Deemed dividend					$ 56,792
Maximum [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Shares of common stock called by warrants									1,659
First Registered Direct Offering [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Shares of common stock issued				286,633
Purchase price per share				$ 17.02
Net proceeds from offering				$ 4,334,816
Placement agent fees and offering expenses				$ 500,000
Unit Offering [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Net proceeds from offering			$ 10,667,505
Common units outstanding			2,400,000
Sale of transaction date			Oct. 02, 2018
Common units issued			2,400,000
Unit Offering [Member] \| Common Units
Changes In Equity And Comprehensive Income Line Items [Line Items]
Public offering price per share			$ 5.00
Per share exercise price			$ 6.00
Warrant expiration period			5 years
Unit Offering [Member] \| Common Units [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Public offering price per share			$ 4.99
Per share exercise price			0.01
Per share exercise price			$ 6.00
Second Registered Direct Offering [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Net proceeds from offering		$ 22,400,673
Common units outstanding		4,629,630
Sale of transaction date		Oct. 10, 2018
Common units issued					4,629,630
Deemed dividend		$ 780,038
Second Registered Direct Offering [Member] \| Maximum [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Per share exercise price		$ 6.00
Second Registered Direct Offering [Member] \| Minimum [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Per share exercise price		4.1798
Second Registered Direct Offering [Member] \| Common Units
Changes In Equity And Comprehensive Income Line Items [Line Items]
Public offering price per share		5.40
Per share exercise price		$ 5.40
Warrant expiration period		5 years
Second Registered Direct Offering [Member] \| Common Units [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Public offering price per share		$ 5.39
Per share exercise price		5.40
Per share exercise price		$ 0.01
Third Registered Direct Offering [Member] \| Subsequent Event [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Net proceeds from offering	$ 12,691,384
Common units outstanding	4,361,370
Sale of transaction date	Mar. 12, 2019
Warrant expiration period	5 years
Third Registered Direct Offering [Member] \| Subsequent Event [Member] \| Maximum [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Per share exercise price	$ 4.1798
Third Registered Direct Offering [Member] \| Subsequent Event [Member] \| Minimum [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Per share exercise price	2.7568
Third Registered Direct Offering [Member] \| Common Units \| Subsequent Event [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Public offering price per share	3.21
Per share exercise price	$ 3.21
Shares of common stock called by warrants	0.70
Third Registered Direct Offering [Member] \| Common Units [Member] \| Subsequent Event [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Public offering price per share	$ 3.20
Per share exercise price	0.01
Per share exercise price	$ 3.21
Shares of common stock called by warrants	0.70