Quarterly Financial Information (Unaudited) Selected Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information [Line Items]
Total revenue	$ 98,947	$ 98,362	$ 84,113	$ 85,319	$ 82,605	$ 82,507	$ 85,023	$ 80,732	$ 366,741	$ 330,867	$ 314,983
Operating income (loss)	29,993	30,384	24,487	28,821	22,091	27,275	17,249	12,920	113,685	79,535	93,646
Net income	16,485	16,519	11,941	15,243	9,209	14,271	4,413	(691)	60,188	27,202	40,132
Net income attributable to restricted shares	(104)	(92)	(92)	(93)	(96)	(71)	(216)	72	(381)	(311)	(241)
Net income attributable to unitholders in the Operating Partnership	(3,536)	(3,565)	(2,933)	(4,055)	(2,440)	(3,806)	(1,125)	166	(14,089)	(7,205)	(10,814)
Net income (loss) attributable to American Assets Trust, Inc. stockholders	$ 12,845	$ 12,862	$ 8,916	$ 11,095	$ 6,673	$ 10,394	$ 3,072	$ (453)	45,718	19,686	29,077
Net income attributable to common stockholders - basic and diluted (in dollars per share)	$ 0.22	$ 0.22	$ 0.18	$ 0.24	$ 0.14	$ 0.22	$ 0.07	$ (0.01)
American Assets Trust, L.P.
Quarterly Financial Information [Line Items]
Total revenue	$ 98,947	$ 98,362	$ 84,113	$ 85,319	$ 82,605	$ 82,507	$ 85,023	$ 80,732	366,741	330,867	314,983
Operating income (loss)	29,993	30,384	24,487	28,821	22,091	27,275	17,249	12,920	113,685	79,535	93,646
Net income	16,485	16,519	11,941	15,243	9,209	14,271	4,413	(691)	60,188	27,202	40,132
Net income attributable to restricted shares	(104)	(92)	(92)	(93)	(96)	(71)	(216)	72	(381)	(311)	(241)
Net income (loss) attributable to American Assets Trust, Inc. stockholders									$ 59,807	$ 26,891	$ 39,891
Net income attributable to American Assets Trust, L.P. unit holders	$ 16,381	$ 16,427	$ 11,849	$ 15,150	$ 9,113	$ 14,200	$ 4,197	$ (619)
Net income attributable to common stockholders - basic and diluted (in dollars per share)	$ 0.22	$ 0.22	$ 0.18	$ 0.24	$ 0.14	$ 0.22	$ 0.07	$ (0.01)