Fair Value of Financial Instruments - Additional Information (Detail)	Dec. 31, 2012
Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Rates of secured notes payable	3.43%
Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Rates of secured notes payable	7.14%

Rate used for discounted cash flow analysis of level two fair values of mortgages and notes payable.

No definition available.

Name:	aat_RateUsedForDiscountedCashFlowAnalysisOfLevelTwoFairValuesOfMortgagesAndNotesPayable
Namespace Prefix:	aat_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant