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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Total segments' profit										$ 198,306	$ 187,157	$ 177,617
General and administrative										(21,382)	(17,897)	(20,074)
Depreciation and amortization										(83,278)	(71,319)	(63,392)
Interest expense										53,848	51,936	47,260
Gain on sale of real estate										0	0	7,121
Other income (expense), net										334	(368)	(97)
Net income	$ 9,731	$ 12,505	$ 7,588	$ 10,308	$ 12,408	$ 11,858	$ 10,650	$ 10,721	$ (3,670)	40,132	45,637	53,915
Net income attributable to restricted shares	(60)	(60)	(61)	(60)	(61)	(42)	(43)	(43)		(241)	(189)	(168)
Net income attributable to unitholders in the Operating Partnership	(2,594)	(3,351)	(2,008)	(2,861)	(3,486)	(3,342)	(3,008)	(3,027)		(10,814)	(12,863)	(15,238)
Net income attributable to American Assets Trust, L.P. unit holders	$ 7,077	$ 9,094	$ 5,519	$ 7,387	$ 8,861	$ 8,474	$ 7,599	$ 7,651		$ 29,077	$ 32,585	$ 38,509