Related Party Transactions - Additional Information (Detail) - Affiliate	3 Months Ended
Mar. 31, 2020
Related Party Transaction [Line Items]
Interest rate on mortgage loans	7.25%
Due date of mortgage loans receivable	Apr. 01, 2019
Moody Foundation \| Gal-Tex
Related Party Transaction [Line Items]
Noncontrolling owners, ownership percentage	34.00%
Moody Foundation \| American National
Related Party Transaction [Line Items]
Noncontrolling owners, ownership percentage	22.75%
Libbie Shearn Moody Trust \| Gal-Tex
Related Party Transaction [Line Items]
Noncontrolling owners, ownership percentage	50.20%
Libbie Shearn Moody Trust \| American National
Related Party Transaction [Line Items]
Noncontrolling owners, ownership percentage	37.00%

Maturity date of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, in CCYY-MM-DD format.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Paragraph Column C
-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column C))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

Name:	srt_MortgageLoanOnRealEstateFinalMaturityDate
Namespace Prefix:	srt_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest rate of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Paragraph Column B
-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column B))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

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- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

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- 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

No definition available.

+ Details

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- Details

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- Details

Name:	dei_LegalEntityAxis=anat_MoodyFoundationMember
Namespace Prefix:
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- Details

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- Details

Name:	srt_OwnershipAxis=anat_AmericanNationalInsuranceCoMember
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- Details

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