SEGMENT REPORTING - Operating Activity Within Reportable Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
OPERATING INCOME	$ 23,244us-gaap_OperatingIncomeLoss	$ 20,381us-gaap_OperatingIncomeLoss
Total Segments' profit	43,367us-gaap_GrossProfit	41,334us-gaap_GrossProfit
Total Retail
Segment Reporting Information [Line Items]
Property revenue	24,038	22,999
Property expense	(6,000)	(6,058)
OPERATING INCOME	18,038	16,941
Total Office
Segment Reporting Information [Line Items]
Property revenue	23,577	22,858
Property expense	(6,821)	(6,893)
OPERATING INCOME	16,756	15,965
Total Multifamily
Segment Reporting Information [Line Items]
Property revenue	4,310	4,130
Property expense	(1,484)	(1,427)
OPERATING INCOME	2,826	2,703
Total Mixed-Use
Segment Reporting Information [Line Items]
Property revenue	14,110	13,993
Property expense	(8,363)	(8,268)
OPERATING INCOME	$ 5,747	$ 5,725

Property expenses.

No definition available.

Name:	aat_PropertyExpenses
Namespace Prefix:	aat_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

+ References

+ Details

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

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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

- Definition

The aggregate revenue from real estate operations during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(e))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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

- Details

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Period Type:	duration

- Details

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Namespace Prefix:
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- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=aat_MultiFamilyMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=aat_OfficeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=aat_RetailMember
Namespace Prefix:
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