Consolidated Statements of Equity - USD ($) $ in Thousands		Total	American Assets Trust, L.P.	Limited Partner American Assets Trust, L.P.	[1]	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, 2017															47,204,588
Beginning balance at Dec. 31, 2017		$ 844,144													$ 473		$ 919,066	$ (97,280)	$ 11,451			$ 10,434
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		27,202	$ 27,202	$ 7,205		$ 19,997	[2]											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)	[2]								(12,686)
Shares withheld for employee taxes		(527)	(527)			$ (527)	[2]								$ 0		(527)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		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)
Beginning balance (in shares) at Dec. 31, 2017				17,194,980		47,204,588	[2]
Beginning balance at Dec. 31, 2017			844,144	$ 6,135		$ 822,259	[2]	15,750
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		27,202	27,202	$ 7,205		$ 19,997	[2]											19,997				7,205
Conversion of operating partnership units (in shares)				(17,372)		17,372	[2]
Conversion of operating partnership units				$ 916		$ (916)	[2]
Issuance of restricted units (in shares)	[2]					205,110
Forfeiture of restricted units (in shares)	[2]					(78,975)
Distributions			(70,228)	$ (18,733)		$ (51,495)	[2]
Stock-based compensation			3,039			$ 3,039	[2]
Shares withheld for employee taxes (in shares)						(12,686)	[2]								(12,686)
Units withheld for employee taxes		(527)	(527)			$ (527)	[2]								$ 0		(527)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		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		47,335,409	[2]
Ending balance at Dec. 31, 2018			802,471	$ (4,477)		$ 792,357	[2]	14,591
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		60,188	60,188	14,089		$ 46,099	[2]											46,099				14,089
Common shares issued (in shares)															11,871,552
Common shares issued		515,354	515,354												$ 118		515,236
Issuance of restricted stock (in shares)															173,008
Issuance of restricted stock		0													$ 2		(2)
Forfeiture of restricted stock (in shares)															(70,641)
Forfeiture of restricted stock		0													$ (1)		1
Conversion of operating partnership units (in shares)															787,060	787,060
Conversion of operating partnership units		0													$ 8		12,979		148			(13,135)
Dividends declared and paid		(80,605)																(61,699)
Dividends declared and paid (noncontrolling interest)																						18,906
Stock-based compensation		4,477															4,477
Shares withheld for employee taxes (in shares)						(28,160)	[2]								(28,160)
Shares withheld for employee taxes		(1,338)	(1,338)			$ (1,338)	[2]								$ 0		(1,338)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		(5,571)							(6,084)	(6,084)	(6,084)	$ 513	$ 513	$ 513						(4,482)	$ 392		(1,602)	$ 121
Reclassification of amortization of forward starting swap included in interest expense		1,304	1,304					1,304											998			306
Ending balance (in shares) at Dec. 31, 2019															60,068,228
Ending balance at Dec. 31, 2019		1,293,672													$ 601		1,452,014	(144,378)	5,680			(20,245)
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		60,188	60,188	$ 14,089		$ 46,099	[2]											46,099				14,089
Contributions from American Assets Trust, Inc. (in shares)	[2]					11,871,552
Contributions from American Assets Trust, Inc.	[2]					$ 515,354
Conversion of operating partnership units (in shares)				(787,060)		787,060	[2]
Conversion of operating partnership units				$ (12,987)		$ 12,987	[2]
Issuance of restricted units (in shares)	[2]					173,008
Forfeiture of restricted units (in shares)	[2]					(70,641)
Distributions			(80,605)	$ (18,906)		$ (61,699)	[2]
Stock-based compensation			4,477			$ 4,477	[2]
Shares withheld for employee taxes (in shares)						(28,160)	[2]								(28,160)
Units withheld for employee taxes		(1,338)	(1,338)			$ (1,338)	[2]								$ 0		(1,338)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		(5,571)							(6,084)	(6,084)	(6,084)	$ 513	$ 513	$ 513						(4,482)	$ 392		(1,602)	$ 121
Reclassification of amortization of forward starting swap included in interest expense		1,304	1,304					1,304											998			306
Ending balance (in shares) at Dec. 31, 2019				16,390,548		60,068,228	[2]
Ending balance at Dec. 31, 2019			1,293,672	$ (22,281)		$ 1,308,237	[2]	7,716
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		35,588	35,588	7,545		$ 28,043	[2]											28,043				7,545
Issuance of restricted stock (in shares)															317,574
Issuance of restricted stock		0													$ 3		(3)
Forfeiture of restricted stock (in shares)															(95,086)
Forfeiture of restricted stock		0													$ (1)		1
Conversion of operating partnership units (in shares)															209,011	209,011
Conversion of operating partnership units		0													$ 2		(12,003)		3			11,998
Dividends declared and paid		(76,510)																(60,225)
Dividends declared and paid (noncontrolling interest)																						16,285
Stock-based compensation		6,307															6,307
Shares withheld for employee taxes (in shares)						(23,435)	[2]								(23,435)
Shares withheld for employee taxes		(672)	(672)			$ (672)	[2]								$ 0		(672)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		(3,649)							(3,649)	(3,649)	(3,649)									(2,885)			(764)
Reclassification of amortization of forward starting swap included in interest expense		1,330	1,330					1,330											1,045			285
Ending balance (in shares) at Dec. 31, 2020															60,476,292
Ending balance at Dec. 31, 2020		1,253,406													$ 605		1,445,644	(176,560)	1,753			(18,036)
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		35,588	35,588	$ 7,545		$ 28,043	[2]											$ 28,043				7,545
Conversion of operating partnership units (in shares)				(209,011)		209,011	[2]
Conversion of operating partnership units				$ 12,001		$ (12,001)	[2]
Issuance of restricted units (in shares)	[2]					317,574
Forfeiture of restricted units (in shares)	[2]					(95,086)
Distributions			(76,510)	$ (16,285)		$ (60,225)	[2]
Stock-based compensation			6,307			$ 6,307	[2]
Shares withheld for employee taxes (in shares)						(23,435)	[2]								(23,435)
Units withheld for employee taxes		(672)	(672)			$ (672)	[2]								$ 0		$ (672)
Other comprehensive income (loss) unrealized gain (loss) on derivatives		(3,649)							$ (3,649)	$ (3,649)	$ (3,649)									$ (2,885)			$ (764)
Reclassification of amortization of forward starting swap included in interest expense		$ 1,330	1,330					1,330											$ 1,045			$ 285
Ending balance (in shares) at Dec. 31, 2020				16,181,537		60,476,292	[2]
Ending balance at Dec. 31, 2020			$ 1,253,406	$ (19,020)		$ 1,269,689	[2]	$ 2,737

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

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