Segment Reporting Reconciliation of Segment Profit to Net Income Attributable to Stockholders (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting [Abstract]
Total segments' profit									$ 223,454	$ 234,761	$ 209,412
General and administrative									(26,581)	(24,871)	(22,784)
Depreciation and amortization									(108,292)	(96,205)	(107,093)
Interest expense									53,440	54,008	52,248
Gain on sale of real estate									0	633	0
Other income (expense), net									447	(122)	(85)
Net income	$ 3,788	$ 6,490	$ 9,826	$ 15,484	$ 16,485	$ 16,519	$ 11,941	$ 15,243	35,588	60,188	27,202
Net income attributable to restricted shares	(123)	(87)	(69)	(104)	(104)	(92)	(92)	(93)	(383)	(381)	(311)
Net income attributable to unitholders in the Operating Partnership	(767)	(1,365)	(2,101)	(3,312)	(3,536)	(3,565)	(2,933)	(4,055)	(7,545)	(14,089)	(7,205)
Net income (loss) attributable to American Assets Trust, Inc. stockholders	$ 2,898	$ 5,038	$ 7,656	$ 12,068	$ 12,845	$ 12,862	$ 8,916	$ 11,095	$ 27,660	$ 45,718	$ 19,686