Segment Reporting Reconciliation of Segment Profit to Net Income Attributable to Stockholders (Details) - USD ($) $ 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
Segment Reporting [Abstract]
Total segments' profit									$ 234,761	$ 209,412	$ 198,306
General and administrative									(24,871)	(22,784)	(21,382)
Depreciation and amortization									(96,205)	(107,093)	(83,278)
Interest expense									54,008	52,248	53,848
Gain on sale of real estate									633	0	0
Other income (expense), net									(122)	(85)	334
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