Net Real Estate and Secured Note Payable Balances for Each Segment (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Excludes unamortized fair market value adjustments	$ 12.3	$ 13.0

Excludes unamortized fair market value adjustments.

No definition available.

Name:	aat_ExcludesUnamortizedFairMarketValueAdjustments
Namespace Prefix:	aat_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant