Mortgage loans on real estate foreclosures process.

No definition available.

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Namespace Prefix:	anat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of mortgage loan foreclosed.

+ References

No definition available.

+ Details

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- Definition

Number of mortgage loan sold.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Number of mortgage loans in foreclosure process.

+ References

No definition available.

+ Details

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- Definition

Unamortized discounts from face amounts of loan.

+ References

No definition available.

+ Details

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- Definition

Unamortized costs incurred to originate loans.

+ 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.

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- Definition

Amount of decrease in 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, from foreclosure.

+ References

Reference 1: 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(Footnote 6))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118956080&loc=d3e11927-110247

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118955202&loc=SL82919202-210446

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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Mortgage Loans - Additional Information (Detail)	3 Months Ended	6 Months Ended	12 Months Ended
Mortgage Loans - Additional Information (Detail)	Mar. 31, 2020 USD ($) loan	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) loan	Jan. 01, 2020 USD ($)
Financing Receivable, Modifications [Line Items]
Number of mortgage loan foreclosed \| loan	0		2
Mortgage loans foreclosed	$ 9,230,000		$ 16,008,000
Number of loans in foreclosure process \| loan			2
Mortgage loans foreclosure process			$ 13,345,000
Number of mortgage loans sold \| loan	0		0
Unamortized discounts	$ 0		$ 0
Unamortized origination fees, mortgage loans	29,231,000	$ 29,294,000
Off balance sheet liability				$ 0
Adjustment to Adopt ASC 326
Financing Receivable, Modifications [Line Items]
Off balance sheet liability				(3,126,000)
Adjustment to Adopt ASC 326 \| Commercial loans
Financing Receivable, Modifications [Line Items]
Off balance sheet liability	6,150,000
Balance as of January 1, 2020
Financing Receivable, Modifications [Line Items]
Off balance sheet liability				$ (3,126,000)
Balance as of January 1, 2020 \| Commercial loans
Financing Receivable, Modifications [Line Items]
Off balance sheet liability	$ 687,287,000