Consolidated Statements of Equity - USD ($) $ in Thousands		Total	American Assets Trust, L.P.	Limited Partner American Assets Trust, L.P.		General Partner American Assets Trust, L.P.		Accumulated Other Comprehensive Income (Loss) American Assets Trust, L.P.	Swap	Swap American Assets Trust, L.P.	Swap Accumulated Other Comprehensive Income (Loss) American Assets Trust, L.P.	Forward Contracts	Forward Contracts American Assets Trust, L.P.	Forward Contracts Accumulated Other Comprehensive Income (Loss) American Assets Trust, L.P.	Common Stock	Common Stock American Assets Trust, L.P.	Additional Paid-in Capital	Accumulated dividends in excess of net income	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Swap	Accumulated Other Comprehensive Income (Loss) Forward Contracts	Noncontrolling Interests - Unitholders in the Operating Partnership	Noncontrolling Interests - Unitholders in the Operating Partnership Swap	Noncontrolling Interests - Unitholders in the Operating Partnership Forward Contracts
Beginning balance (in shares) at Dec. 31, 2015															45,407,719
Beginning balance at Dec. 31, 2015		$ 828,927													$ 454		$ 863,432	$ (64,066)	$ (258)			$ 29,365
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		45,637	$ 45,637	$ 12,863	[1]	$ 32,774	[2]											32,774				12,863
Common shares issued (in shares)															219,480
Common shares issued		9,640													$ 2		9,638
Issuance of restricted stock (in shares)															148,110
Issuance of restricted stock		0													$ 1		(1)
Forfeiture of restricted stock (in shares)															(33,707)
Forfeiture of restricted stock		0													$ 0		0
Conversion of operating partnership units (in shares)															10,694	10,694
Conversion of operating partnership units		0															(79)					79
Dividends declared and paid		(64,077)																(46,004)
Dividends declared and paid (noncontrolling interest)																						18,073
Stock-based compensation		2,414															2,414
Shares withheld for employee taxes (in shares)						(20,187)	[2]								(20,187)
Shares withheld for employee taxes		(807)	(807)			$ (807)	[2]								$ 0		(807)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		17,048	17,048						$ 17,048	$ 17,048	$ 17,048									$ 12,222			$ 4,826
Reclassification of amortization of forward starting swap included in interest expense		231	231					$ 231											166			65
Ending balance (in shares) at Dec. 31, 2016															45,732,109
Ending balance at Dec. 31, 2016		838,551													$ 457		874,597	(77,296)	11,798			28,995
Beginning balance (in shares) at Dec. 31, 2015				17,899,516	[1]	45,407,719	[2]
Beginning balance at Dec. 31, 2015			828,927	$ 29,446	[1]	$ 799,820	[2]	(339)
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		45,637	45,637	$ 12,863	[1]	$ 32,774	[2]											32,774				12,863
Contributions from American Assets Trust, Inc. (in shares)	[2]					219,480
Contributions from American Assets Trust, Inc.			9,640			$ 9,640	[2]
Conversion of operating partnership units (in shares)				(10,694)	[1]	10,694	[2]
Conversion of operating partnership units				$ 79	[1]	$ (79)	[2]
Issuance of restricted units (in shares)	[2]					148,110
Forfeiture of restricted units (in shares)	[2]					(33,707)
Distributions			(64,077)	$ (18,073)	[1]	$ (46,004)	[2]
Stock-based compensation			2,414			$ 2,414	[2]
Shares withheld for employee taxes (in shares)						(20,187)	[2]								(20,187)
Units withheld for employee taxes		(807)	(807)			$ (807)	[2]								$ 0		(807)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		17,048	17,048						17,048	17,048	17,048									12,222			4,826
Reclassification of amortization of forward starting swap included in interest expense		231	231					231											166			65
Ending balance (in shares) at Dec. 31, 2016				17,888,822	[1]	45,732,109	[2]
Ending balance at Dec. 31, 2016			838,551	$ 24,315	[1]	$ 797,758	[2]	16,478
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		40,132	40,132	10,814	[1]	$ 29,318	[2]											29,318				10,814
Common shares issued (in shares)															700,000
Common shares issued		29,873													$ 7		29,866
Issuance of restricted stock (in shares)															150,098
Issuance of restricted stock		0													$ 2		(2)
Forfeiture of restricted stock (in shares)															(48,624)
Forfeiture of restricted stock		0													$ 0		0
Conversion of operating partnership units (in shares)															693,842	693,842
Conversion of operating partnership units		0													$ 7		10,752					(10,759)
Dividends declared and paid		(67,537)																(49,302)
Dividends declared and paid (noncontrolling interest)																						18,235
Stock-based compensation		4,735															4,735
Shares withheld for employee taxes (in shares)						(22,837)	[2]								(22,837)
Shares withheld for employee taxes		(882)	(882)			$ (882)	[2]								$ 0		(882)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		386	386						(10,281)	(10,281)	(10,281)	$ 10,667	$ 10,667	$ 10,667						(7,310)	$ 7,775		(2,971)	$ 2,892
Reclassification of amortization of forward starting swap included in interest expense		1,114	1,114					1,114											812			302
Ending balance (in shares) at Dec. 31, 2017															47,204,588
Ending balance at Dec. 31, 2017		844,144													$ 473		919,066	(97,280)	11,451			10,434
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		40,132	40,132	$ 10,814	[1]	$ 29,318	[2]											29,318				10,814
Contributions from American Assets Trust, Inc. (in shares)	[2]					700,000
Contributions from American Assets Trust, Inc.			29,873			$ 29,873	[2]
Conversion of operating partnership units (in shares)				(693,842)	[1]	693,842	[2]
Conversion of operating partnership units				$ (10,759)	[1]	$ 10,759	[2]
Issuance of restricted units (in shares)	[2]					150,098
Forfeiture of restricted units (in shares)	[2]					(48,624)
Distributions			(67,537)	$ (18,235)	[1]	$ (49,302)	[2]
Stock-based compensation			4,735			$ 4,735	[2]
Shares withheld for employee taxes (in shares)						(22,837)	[2]								(22,837)
Units withheld for employee taxes		(882)	(882)			$ (882)	[2]								$ 0		(882)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		386	386						(10,281)	(10,281)	(10,281)	$ 10,667	$ 10,667	$ 10,667						(7,310)	$ 7,775		(2,971)	$ 2,892
Reclassification of amortization of forward starting swap included in interest expense		1,114	1,114					1,114											812			302
Ending balance (in shares) at Dec. 31, 2017				17,194,980	[1]	47,204,588	[2]
Ending balance at Dec. 31, 2017			844,144	$ 6,135	[1]	$ 822,259	[2]	15,750
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		27,202	27,202	7,205		$ 19,997												19,997				7,205
Issuance of restricted stock (in shares)															205,110
Issuance of restricted stock		0													$ 2		(2)
Forfeiture of restricted stock (in shares)															(78,975)
Forfeiture of restricted stock		0													$ (1)		1
Conversion of operating partnership units (in shares)															17,372	17,372
Conversion of operating partnership units		0													$ 0		(916)					916
Dividends declared and paid		(70,228)																(51,495)
Dividends declared and paid (noncontrolling interest)																						18,733
Stock-based compensation		3,039															3,039
Shares withheld for employee taxes (in shares)						(12,686)									(12,686)
Shares withheld for employee taxes		(527)	(527)			$ (527)									$ 0		(527)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		120	120						120	120	120									105			15
Reclassification of amortization of forward starting swap included in interest expense		1,279	1,279					1,279											936			343
Ending balance (in shares) at Dec. 31, 2018															47,335,409
Ending balance at Dec. 31, 2018		802,471													$ 474		920,661	(128,778)	10,620			(506)
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		27,202	27,202	$ 7,205		$ 19,997												$ 19,997				7,205
Conversion of operating partnership units (in shares)				(17,372)		17,372
Conversion of operating partnership units				$ 916		$ (916)
Issuance of restricted units (in shares)						205,110
Forfeiture of restricted units (in shares)						(78,975)
Distributions			(70,228)	$ (18,733)		$ (51,495)
Stock-based compensation			3,039			$ 3,039
Shares withheld for employee taxes (in shares)						(12,686)									(12,686)
Units withheld for employee taxes		(527)	(527)			$ (527)									$ 0		$ (527)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		120	120						$ 120	$ 120	$ 120									$ 105			$ 15
Reclassification of amortization of forward starting swap included in interest expense		$ 1,279	1,279					1,279											$ 936			$ 343
Ending balance (in shares) at Dec. 31, 2018				17,177,608	[1]	47,335,409	[2]
Ending balance at Dec. 31, 2018			$ 802,471	$ (4,477)	[1]	$ 792,357	[2]	$ 14,591

[1] Consists of limited partnership interests held by third parties.

[2] Consists of general and limited partnership interests held by American Assets Trust, Inc.