EQUITY OF AMERICAN ASSETS TRUST, INC. - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Equity [Abstract]
Net income from operations	$ 19,026	$ 9,090	$ 42,689	$ 21,099
Less: Net income attributable to restricted shares	(32)	(95)	(115)	(259)
Less: Income from continuing operations attributable to unitholders in the Operating Partnership	(5,432)	(2,578)	(12,277)	(6,108)
Net income attributable to common stockholders—basic	13,562	6,417	30,297	14,732
Income from operations attributable to American Assets Trust, Inc. common stockholders—basic	13,562	6,417	30,297	14,732
Net income attributable to common stockholders-diluted	$ 18,994	$ 8,995	$ 42,574	$ 20,840
Weighted average common shares outstanding-basic	44,998,281	42,539,019	44,176,007	41,653,229
Effect of dilutive securities-conversion of Operating Partnership units	17,899,516	17,905,257	17,900,231	17,906,715
Weighted average common shares outstanding - diluted	62,897,797	60,444,276	62,076,238	59,559,944
Earnings per common share, basic (in USD per share)	$ 0.30	$ 0.15	$ 0.69	$ 0.35
Earnings per common share, diluted (in USD per share)	$ 0.30	$ 0.15	$ 0.69	$ 0.35