Quarterly Financial Information (Unaudited) Selected Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information [Line Items]
Total revenue	$ 101,747	$ 98,286	$ 91,809	$ 83,986	$ 81,347	$ 84,374	$ 82,109	$ 96,743	$ 375,828	$ 344,573	$ 366,741
Operating income (loss)	25,715	27,669	26,423	20,062	16,415	20,323	22,995	28,848	99,869	88,581	113,685
Net income	10,478	12,895	11,487	1,733	3,788	6,490	9,826	15,484	36,593	35,588	60,188
Net income attributable to restricted shares	(147)	(145)	(135)	(137)	(123)	(87)	(69)	(104)	(564)	(383)	(381)
Net income attributable to unitholders in the Operating Partnership	(2,194)	(2,709)	(2,411)	(339)	(767)	(1,365)	(2,101)	(3,312)	(7,653)	(7,545)	(14,089)
Net income attributable to American Assets Trust, Inc. stockholders	$ 8,137	$ 10,041	$ 8,941	$ 1,257	$ 2,898	$ 5,038	$ 7,656	$ 12,068
Net income attributable to common stockholders - basic and diluted (in dollars per share)	$ 0.14	$ 0.17	$ 0.15	$ 0.02	$ 0.05	$ 0.08	$ 0.13	$ 0.20
American Assets Trust, L.P.
Quarterly Financial Information [Line Items]
Total revenue	$ 101,747	$ 98,286	$ 91,809	$ 83,986	$ 81,347	$ 84,374	$ 82,109	$ 96,743	375,828	344,573	366,741
Operating income (loss)	25,715	27,669	26,423	20,062	16,415	20,323	22,995	28,848	99,869	88,581	113,685
Net income	10,478	12,895	11,487	1,733	3,788	6,490	9,826	15,484	36,593	35,588	60,188
Net income attributable to restricted shares	(147)	(145)	(135)	(137)	(123)	(87)	(69)	(104)	$ (564)	$ (383)	$ (381)
Net income attributable to American Assets Trust, L.P. unit holders	$ 10,331	$ 12,750	$ 11,352	$ 1,596	$ 3,665	$ 6,403	$ 9,757	$ 15,380
Net income attributable to common stockholders - basic and diluted (in dollars per share)	$ 0.14	$ 0.17	$ 0.15	$ 0.02	$ 0.05	$ 0.08	$ 0.13	$ 0.20