Segment Reporting Reconciliation of Segment Profit to Net Income Attributable to Stockholders (Details) - USD ($) $ in Thousands	3 Months Ended								8 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Total segments' profit										$ 209,412	$ 198,306	$ 187,157
General and administrative										(22,784)	(21,382)	(17,897)
Depreciation and amortization										(107,093)	(83,278)	(71,319)
Interest expense										52,248	53,848	51,936
Other income (expense), net										(85)	334	(368)
Net income	$ 9,209	$ 14,271	$ 4,413	$ (691)	$ 9,731	$ 12,505	$ 7,588	$ 10,308	$ (3,670)	27,202	40,132	45,637
Net income attributable to restricted shares	(96)	(71)	(216)	72	(60)	(60)	(61)	(60)		(311)	(241)	(189)
Net income attributable to unitholders in the Operating Partnership	(2,440)	(3,806)	(1,125)	166	(2,594)	(3,351)	(2,008)	(2,861)		(7,205)	(10,814)	(12,863)
Net income attributable to American Assets Trust, Inc. stockholders	$ 6,673	$ 10,394	$ 3,072	$ (453)	$ 7,077	$ 9,094	$ 5,519	$ 7,387		$ 19,686	$ 29,077	$ 32,585