Allocated share based compensation expense credit.

No definition available.

Name:	anat_AllocatedShareBasedCompensationExpenseCredit
Namespace Prefix:	anat_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award equity instruments other than options exercisable number.

+ References

No definition available.

+ Details

Name:	anat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableNumber
Namespace Prefix:	anat_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the share-based compensation plan for those exercisable shares.

+ References

No definition available.

+ Details

Name:	anat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisableWeightedAverageExercisePrice
Namespace Prefix:	anat_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average fair value at grant date or for equity-based award exercised during the period other than stock option plans.

+ References

No definition available.

+ Details

Name:	anat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	anat_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Expired In Period Weighted Average Grant Date Fair Value

+ References

No definition available.

+ Details

Name:	anat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpiredInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	anat_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award equity instruments other than options fair value of liability component of award.

+ References

No definition available.

+ Details

Name:	anat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsFairValueOfLiabilityComponentOfAward
Namespace Prefix:	anat_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the share-based compensation plan.

+ References

No definition available.

+ Details

Name:	anat_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageExercisePrice
Namespace Prefix:	anat_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

+ Details

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

- Definition

Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of non-option equity instruments exercised by participants.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised
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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares under non-option equity instrument agreements that were either cancelled or expired.

+ References

+ Details

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

- Definition

Net number of non-option equity instruments granted to participants.

+ References

+ Details

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

- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_StockAppreciationRightsSARSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stockholders' Equity and Noncontrolling Interests - Stock-Based Compensation Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Stock Appreciation Rights
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance, shares			335
Forfeited, shares			(269)
Ending balance, shares	66		66
Weighted-Average Grant Date Fair Value, Beginning balance			$ 84.41
Weighted-Average Grant Date Fair Value, Expired			77.90
Weighted-Average Grant Date Fair Value, Ending balance	$ 110.83		$ 110.83
Weighted-average contractual remaining life (in years)			17 days
Exercisable shares	66		66
Weighted-average exercise price			$ 110.83
Weighted-average exercise price exercisable shares	$ 110.83		$ 110.83
Compensation expense (credit)	$ 1,000	$ 7,000	$ (14,000)	$ (27,000)
Fair value of liability award	$ 1,000		$ 1,000		$ 33,000
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance, shares			10,000
Ending balance, shares	10,000		10,000
Weighted-Average Grant Date Fair Value, Beginning balance			$ 80.05
Weighted-Average Grant Date Fair Value, Ending balance	$ 80.05		$ 80.05
Weighted-average contractual remaining life (in years)			3 years 5 months 1 day
Weighted-average exercise price			$ 80.05
Compensation expense (credit)	$ 20,000	24,000	$ 60,000	308,000
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance, shares			18,316
Granted, shares			8,250
Exercised, shares			(18,316)
Ending balance, shares	8,250		8,250
Weighted-Average Grant Date Fair Value, Beginning balance			$ 111.12
Weighted-Average Grant Date Fair Value, Granted			113.19
Weighted-Average Grant Date Fair Value, Exercised			111.12
Weighted-Average Grant Date Fair Value, Ending balance	$ 113.19		$ 113.19
Weighted-average contractual remaining life (in years)			17 days
Weighted-average exercise price			$ 111.12
Compensation expense (credit)	$ 154,000	$ 371,000	$ 1,094,000	$ 920,000
Fair value of liability award	$ 1,021,000		$ 1,021,000		$ 2,426,000