Consolidated Statement of Equity (Unaudited) - USD ($) $ in Thousands		Total	American Assets Trust, L.P.	American Assets Trust, L.P. Accumulated Other Comprehensive Income (Loss)	American Assets Trust, L.P. Limited Partner		American Assets Trust, L.P. General Partner		Common Shares	Common Shares American Assets Trust, L.P.	Common Shares American Assets Trust, L.P. Limited Partner	Additional Paid-in Capital	Accumulated Dividends in Excess of Net Income	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests - Unitholders in the Operating Partnership	Swap	Swap American Assets Trust, L.P.	Swap American Assets Trust, L.P. Accumulated Other Comprehensive Income (Loss)	Swap Accumulated Other Comprehensive Income (Loss)	Swap Noncontrolling Interests - Unitholders in the Operating Partnership	Forward Contracts	Forward Contracts American Assets Trust, L.P.	Forward Contracts American Assets Trust, L.P. Accumulated Other Comprehensive Income (Loss)	Forward Contracts Accumulated Other Comprehensive Income (Loss)	Forward Contracts Noncontrolling Interests - Unitholders in the Operating Partnership
Beginning Balance (shares) at Dec. 31, 2018									47,335,409
Beginning Balance at Dec. 31, 2018		$ 802,471							$ 474			$ 920,661	$ (128,778)	$ 10,620	$ (506)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		15,243	$ 15,243		$ 4,055	[1]	$ 11,188	[2]					11,188		4,055
Common shares issued (shares)									162,531
Common shares issued		7,034	7,034						$ 1			7,033
Forfeiture of restricted stock (shares)									(11,046)
Dividends declared and paid		(18,061)											(13,251)
Dividends declared and paid (noncontrolling interest)															(4,810)
Stock-based compensation		1,098										1,098
Other comprehensive loss - change in value of interest rate swaps																$ (2,132)	$ (2,132)	$ (2,132)	$ (1,561)	$ (571)
Reclassification of amortization of forward-starting swap included in interest expense		(320)	(320)	$ (320)										(234)	(86)
Ending Balance (shares) at Mar. 31, 2019									47,486,894
Ending Balance at Mar. 31, 2019		805,333							$ 475			928,792	(130,841)	8,825	(1,918)
Beginning partners' capital account (shares) at Dec. 31, 2018					17,177,608	[1]	47,335,409	[2]
Beginning partners' capital account at Dec. 31, 2018			802,471	14,591	$ (4,477)	[1]	$ 792,357	[2]
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		15,243	15,243		4,055	[1]	$ 11,188	[2]					11,188		4,055
Contributions from American Assets Trust, Inc. (in shares)							162,531
Contributions from American Assets Trust, Inc.							$ 7,034
Forfeiture of restricted units	[2]						(11,046)
Distributions			(18,061)		$ (4,810)	[1]	$ (13,251)	[2]
Stock-based compensation			1,098				$ 1,098	[2]
Other comprehensive loss - change in value of interest rate swaps																(2,132)	(2,132)	(2,132)	(1,561)	(571)
Reclassification of amortization of forward-starting swap included in interest expense		(320)	(320)	(320)										(234)	(86)
Ending partners' capital account (shares) at Mar. 31, 2019					17,177,608	[1]	47,486,894	[2]
Ending partners' capital account at Mar. 31, 2019			805,333	12,139	$ (5,232)	[1]	$ 798,426	[2]
Beginning Balance (shares) at Dec. 31, 2018									47,335,409
Beginning Balance at Dec. 31, 2018		802,471							$ 474			920,661	(128,778)	10,620	(506)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		43,703	43,703
Other comprehensive income - unrealized gain on forward-starting interest rate swaps																					$ 513	$ 513
Reclassification of amortization of forward-starting swap included in interest expense		(972)	(972)
Ending Balance (shares) at Sep. 30, 2019									59,956,972
Ending Balance at Sep. 30, 2019		1,298,224							$ 599			1,450,816	(139,307)	5,162	(19,046)
Beginning partners' capital account (shares) at Dec. 31, 2018					17,177,608	[1]	47,335,409	[2]
Beginning partners' capital account at Dec. 31, 2018			802,471	14,591	$ (4,477)	[1]	$ 792,357	[2]
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		43,703	43,703
Reclassification of amortization of forward-starting swap included in interest expense		(972)	(972)
Ending partners' capital account (shares) at Sep. 30, 2019					16,390,548	[1]	59,956,972	[2]
Ending partners' capital account at Sep. 30, 2019			1,298,224	7,015	$ (20,899)	[1]	$ 1,312,108	[2]
Beginning Balance (shares) at Mar. 31, 2019									47,486,894
Beginning Balance at Mar. 31, 2019		805,333							$ 475			928,792	(130,841)	8,825	(1,918)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		11,941	11,941		$ 2,933	[1]	$ 9,008	[2]					9,008		2,933
Common shares issued (shares)									11,444,382
Common shares issued		495,980	495,980						$ 114			495,866
Issuance of restricted stock (shares)							4,412		4,412
Conversion of operating partnership units (in shares)									787,060
Conversion of operating partnership units									$ 8			12,979		148	(13,135)
Dividends declared and paid		(18,253)											(13,664)
Dividends declared and paid (noncontrolling interest)															(4,589)
Stock-based compensation		1,131										1,131
Other comprehensive loss - change in value of interest rate swaps																(3,891)	(3,891)	(3,891)	(2,857)	(1,034)
Other comprehensive income - unrealized gain on forward-starting interest rate swaps																					513	513
Reclassification of amortization of forward-starting swap included in interest expense		(319)	(319)	(319)										(240)	(79)
Ending Balance (shares) at Jun. 30, 2019									59,722,748
Ending Balance at Jun. 30, 2019		1,291,922							$ 597			1,438,768	(135,497)	5,876	(17,822)
Beginning partners' capital account (shares) at Mar. 31, 2019					17,177,608	[1]	47,486,894	[2]
Beginning partners' capital account at Mar. 31, 2019			805,333	12,139	$ (5,232)	[1]	$ 798,426	[2]
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		11,941	11,941		2,933	[1]	$ 9,008	[2]					9,008		2,933
Contributions from American Assets Trust, Inc. (in shares)							11,444,382
Contributions from American Assets Trust, Inc.							$ 495,980
Issuance of restricted stock (shares)							4,412		4,412
Conversion of operating partnership units (shares)							787,060	[2]			(787,060)
Conversion of operating partnership units							$ 12,987				$ (12,987)
Distributions			(18,253)		$ (4,589)	[1]	(13,664)	[2]
Stock-based compensation			1,131				$ 1,131	[2]
Other comprehensive loss - change in value of interest rate swaps																(3,891)	(3,891)	(3,891)	(2,857)	(1,034)
Reclassification of amortization of forward-starting swap included in interest expense		(319)	(319)	(319)										(240)	(79)
Ending partners' capital account (shares) at Jun. 30, 2019					16,390,548	[1]	59,722,748	[2]
Ending partners' capital account at Jun. 30, 2019			1,291,922	7,929	$ (19,875)	[1]	$ 1,303,868	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		16,519	16,519		3,565	[1]	12,954	[2]					12,954		3,565
Common shares issued (shares)									234,814
Common shares issued		10,920	10,920						$ 2			10,918
Forfeiture of restricted stock (shares)									(590)
Dividends declared and paid		(21,353)											(16,764)
Dividends declared and paid (noncontrolling interest)															(4,589)
Stock-based compensation		1,130										1,130
Other comprehensive loss - change in value of interest rate swaps																(1,094)	(1,094)	(1,094)	(841)	(253)
Other comprehensive income - unrealized gain on forward-starting interest rate swaps																					513	513	$ 513	$ 388	$ 125
Reclassification of amortization of forward-starting swap included in interest expense		(333)	(333)	(333)										(261)	(72)
Ending Balance (shares) at Sep. 30, 2019									59,956,972
Ending Balance at Sep. 30, 2019		1,298,224							$ 599			1,450,816	(139,307)	5,162	(19,046)
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		16,519	16,519		3,565	[1]	$ 12,954	[2]					12,954		3,565
Contributions from American Assets Trust, Inc. (in shares)							234,814
Contributions from American Assets Trust, Inc.							$ 10,920
Forfeiture of restricted units	[2]						(590)
Distributions			(21,353)		$ (4,589)	[1]	$ (16,764)	[2]
Stock-based compensation			1,130				$ 1,130	[2]
Other comprehensive loss - change in value of interest rate swaps																(1,094)	(1,094)	(1,094)	(841)	(253)
Reclassification of amortization of forward-starting swap included in interest expense		(333)	(333)	(333)										(261)	(72)
Ending partners' capital account (shares) at Sep. 30, 2019					16,390,548	[1]	59,956,972	[2]
Ending partners' capital account at Sep. 30, 2019			1,298,224	7,015	$ (20,899)	[1]	$ 1,312,108	[2]
Beginning Balance (shares) at Dec. 31, 2019									60,068,228
Beginning Balance at Dec. 31, 2019		1,293,672							$ 601			1,452,014	(144,378)	5,680	(20,245)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		15,484	15,484		$ 3,312	[1]	$ 12,172	[2]					12,172		3,312
Dividends declared and paid		(22,937)											(18,020)
Dividends declared and paid (noncontrolling interest)															(4,917)
Stock-based compensation		1,250										1,250
Other comprehensive loss - change in value of interest rate swaps																(6,115)	(6,115)	(6,115)	(4,816)	(1,299)
Reclassification of amortization of forward-starting swap included in interest expense		(333)	(333)	(333)										(261)	(72)
Ending Balance (shares) at Mar. 31, 2020									60,068,228
Ending Balance at Mar. 31, 2020		1,281,021							$ 601			1,453,264	(150,226)	603	(23,221)
Beginning partners' capital account (shares) at Dec. 31, 2019					16,390,548		60,068,228
Beginning partners' capital account at Dec. 31, 2019			1,293,672	7,716	$ (22,281)		$ 1,308,237
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		15,484	15,484		3,312	[1]	12,172	[2]					12,172		3,312
Distributions			(22,937)		$ (4,917)	[1]	(18,020)	[2]
Stock-based compensation			1,250				$ 1,250	[2]
Other comprehensive loss - change in value of interest rate swaps																(6,115)	(6,115)	(6,115)	(4,816)	(1,299)
Reclassification of amortization of forward-starting swap included in interest expense		(333)	(333)	(333)										(261)	(72)
Ending partners' capital account (shares) at Mar. 31, 2020					16,390,548		60,068,228
Ending partners' capital account at Mar. 31, 2020			1,281,021	1,268	$ (23,886)		$ 1,303,639
Beginning Balance (shares) at Dec. 31, 2019									60,068,228
Beginning Balance at Dec. 31, 2019		1,293,672							$ 601			1,452,014	(144,378)	5,680	(20,245)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		31,800	31,800
Conversion of operating partnership units (in shares)										209,011
Other comprehensive income - unrealized gain on forward-starting interest rate swaps																					0	0
Reclassification of amortization of forward-starting swap included in interest expense		(997)	(997)
Ending Balance (shares) at Sep. 30, 2020									60,282,929
Ending Balance at Sep. 30, 2020		1,265,982							$ 603			1,443,764	(164,462)	1,034	(14,957)
Beginning partners' capital account (shares) at Dec. 31, 2019					16,390,548		60,068,228
Beginning partners' capital account at Dec. 31, 2019			1,293,672	7,716	$ (22,281)		$ 1,308,237
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		31,800	31,800
Reclassification of amortization of forward-starting swap included in interest expense		(997)	(997)
Ending partners' capital account (shares) at Sep. 30, 2020					16,181,537		60,282,929
Ending partners' capital account at Sep. 30, 2020			1,265,982	1,819	$ (15,742)		$ 1,279,905
Beginning Balance (shares) at Mar. 31, 2020									60,068,228
Beginning Balance at Mar. 31, 2020		1,281,021							$ 601			1,453,264	(150,226)	603	(23,221)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		9,826	9,826		$ 2,101		$ 7,725						7,725		2,101
Issuance of restricted stock (shares)							6,008		6,008
Forfeiture of restricted stock (shares)									(318)
Dividends declared and paid		(15,293)											(12,015)
Dividends declared and paid (noncontrolling interest)															(3,278)
Stock-based compensation		1,252										1,252
Other comprehensive loss - change in value of interest rate swaps																14	14	14	10	4
Other comprehensive income - unrealized gain on forward-starting interest rate swaps																					$ 0	$ 0
Reclassification of amortization of forward-starting swap included in interest expense		(332)	(332)	(332)										(261)	(71)
Ending Balance (shares) at Jun. 30, 2020									60,073,918
Ending Balance at Jun. 30, 2020		1,276,488							$ 601			1,454,516	(154,516)	352	(24,465)
Beginning partners' capital account (shares) at Mar. 31, 2020					16,390,548		60,068,228
Beginning partners' capital account at Mar. 31, 2020			1,281,021	1,268	$ (23,886)		$ 1,303,639
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		9,826	9,826		2,101		$ 7,725						7,725		2,101
Issuance of restricted stock (shares)							6,008		6,008
Forfeiture of restricted units							(318)
Distributions			(15,293)		$ (3,278)		$ (12,015)
Stock-based compensation			1,252				$ 1,252
Other comprehensive loss - change in value of interest rate swaps																14	14	14	10	4
Reclassification of amortization of forward-starting swap included in interest expense		(332)	(332)	(332)										(261)	(71)
Ending partners' capital account (shares) at Jun. 30, 2020					16,390,548		60,073,918
Ending partners' capital account at Jun. 30, 2020			1,276,488	950	$ (25,063)		$ 1,300,601
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		6,490	6,490		1,365		5,125						5,125		1,365
Conversion of operating partnership units (in shares)									209,011
Conversion of operating partnership units									$ 2			(12,003)		3	11,998
Dividends declared and paid		(19,116)											(15,071)
Dividends declared and paid (noncontrolling interest)															(4,045)
Stock-based compensation		1,251										1,251
Other comprehensive loss - change in value of interest rate swaps																1,201	1,201	1,201	940	261
Reclassification of amortization of forward-starting swap included in interest expense		(332)	(332)	(332)										(261)	(71)
Ending Balance (shares) at Sep. 30, 2020									60,282,929
Ending Balance at Sep. 30, 2020		1,265,982							$ 603			$ 1,443,764	(164,462)	1,034	(14,957)
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		6,490	6,490		1,365		$ 5,125						$ 5,125		1,365
Conversion of operating partnership units (shares)							209,011				(209,011)
Conversion of operating partnership units							$ (12,001)				$ 12,001
Distributions			(19,116)		$ (4,045)		(15,071)
Stock-based compensation			1,251				$ 1,251
Other comprehensive loss - change in value of interest rate swaps																$ 1,201	$ 1,201	$ 1,201	$ 940	$ 261
Reclassification of amortization of forward-starting swap included in interest expense		$ (332)	(332)	(332)										$ (261)	$ (71)
Ending partners' capital account (shares) at Sep. 30, 2020					16,181,537		60,282,929
Ending partners' capital account at Sep. 30, 2020			$ 1,265,982	$ 1,819	$ (15,742)		$ 1,279,905

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

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