Consolidated Statement of Equity (Unaudited) - USD ($)		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
Beginning Balance (shares) at Dec. 31, 2018									47,335,409
Beginning Balance at Dec. 31, 2018		$ 802,471,000							$ 474,000			$ 920,661,000	$ (128,778,000)	$ 10,620,000	$ (506,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		15,243,000	$ 15,243,000		$ 4,055,000	[1]	$ 11,188,000	[2]					11,188,000		4,055,000
Common shares issued (shares)									162,531
Common shares issued		7,034,000	7,034,000						$ 1,000			7,033,000
Forfeiture of restricted stock (shares)									(11,046)
Dividends declared and paid		(18,061,000)											(13,251,000)
Dividends declared and paid (noncontrolling interest)															(4,810,000)
Stock-based compensation		1,098,000										1,098,000
Other comprehensive loss - change in value of interest rate swaps																$ (2,132,000)	$ (2,132,000)	$ (2,132,000)	$ (1,561,000)	$ (571,000)
Reclassification of amortization of forward-starting swap included in interest expense		320,000	320,000	$ 320,000										234,000	86,000
Ending Balance (shares) at Mar. 31, 2019									47,486,894
Ending Balance at Mar. 31, 2019		805,333,000							$ 475,000			928,792,000	(130,841,000)	8,825,000	(1,918,000)
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			802,471,000	14,591,000	$ (4,477,000)	[1]	$ 792,357,000	[2]
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		15,243,000	15,243,000		4,055,000	[1]	$ 11,188,000	[2]					11,188,000		4,055,000
Contributions from American Assets Trust, Inc. (in shares)							162,531
Contributions from American Assets Trust, Inc.							$ 7,034,000
Forfeiture of restricted units	[2]						(11,046)
Distributions			(18,061,000)		$ (4,810,000)	[1]	$ (13,251,000)	[2]
Stock-based compensation			1,098,000				$ 1,098,000	[2]
Other comprehensive loss - change in value of interest rate swaps																(2,132,000)	(2,132,000)	(2,132,000)	(1,561,000)	(571,000)
Reclassification of amortization of forward-starting swap included in interest expense		320,000	320,000	320,000										234,000	86,000
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			805,333,000	12,139,000	$ (5,232,000)	[1]	$ 798,426,000	[2]
Beginning Balance (shares) at Dec. 31, 2018									47,335,409
Beginning Balance at Dec. 31, 2018		802,471,000							$ 474,000			920,661,000	(128,778,000)	10,620,000	(506,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		27,184,000	27,184,000
Reclassification of amortization of forward-starting swap included in interest expense		639,000	639,000
Ending Balance (shares) at Jun. 30, 2019									59,722,748
Ending Balance at Jun. 30, 2019		1,291,922,000							$ 597,000			1,438,768,000	(135,497,000)	5,876,000	(17,822,000)
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			802,471,000	14,591,000	$ (4,477,000)	[1]	$ 792,357,000	[2]
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		27,184,000	27,184,000
Reclassification of amortization of forward-starting swap included in interest expense		639,000	639,000
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			1,291,922,000	7,929,000	$ (19,875,000)	[1]	$ 1,303,868,000	[2]
Beginning Balance (shares) at Mar. 31, 2019									47,486,894
Beginning Balance at Mar. 31, 2019		805,333,000							$ 475,000			928,792,000	(130,841,000)	8,825,000	(1,918,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		11,941,000	11,941,000		$ 2,933,000	[1]	$ 9,008,000	[2]					9,008,000		2,933,000
Common shares issued (shares)									11,444,382
Common shares issued		495,980,000	495,980,000						$ 114,000			495,866,000
Issuance of restricted stock (shares)									4,412
Conversion of operating partnership units (in shares)									787,060
Conversion of operating partnership units									$ 8,000			12,979,000		148,000	(13,135,000)
Dividends declared and paid		(18,253,000)											(13,664,000)
Dividends declared and paid (noncontrolling interest)															(4,589,000)
Stock-based compensation		1,131,000										1,131,000
Other comprehensive loss - change in value of interest rate swaps																(3,891,000)	(3,891,000)	(3,891,000)	(2,857,000)	(1,034,000)
Reclassification of amortization of forward-starting swap included in interest expense		319,000	319,000	319,000										240,000	79,000
Ending Balance (shares) at Jun. 30, 2019									59,722,748
Ending Balance at Jun. 30, 2019		1,291,922,000							$ 597,000			1,438,768,000	(135,497,000)	5,876,000	(17,822,000)
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			805,333,000	12,139,000	$ (5,232,000)	[1]	$ 798,426,000	[2]
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		11,941,000	11,941,000		2,933,000	[1]	$ 9,008,000	[2]					9,008,000		2,933,000
Contributions from American Assets Trust, Inc. (in shares)							11,444,382
Contributions from American Assets Trust, Inc.							$ 495,980,000
Issuance of restricted units							$ 4,412
Conversion of operating partnership units (shares)							787,060	[2]			(787,060)
Conversion of operating partnership units							$ 12,987,000				$ (12,987,000)
Distributions			(18,253,000)		$ (4,589,000)	[1]	(13,664,000)	[2]
Stock-based compensation			1,131,000				$ 1,131,000	[2]
Other comprehensive loss - change in value of interest rate swaps																(3,891,000)	(3,891,000)	(3,891,000)	(2,857,000)	(1,034,000)
Reclassification of amortization of forward-starting swap included in interest expense		319,000	319,000	319,000										240,000	79,000
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			1,291,922,000	7,929,000	$ (19,875,000)	[1]	$ 1,303,868,000	[2]
Beginning Balance (shares) at Dec. 31, 2019									60,068,228
Beginning Balance at Dec. 31, 2019		1,293,672,000							$ 601,000			1,452,014,000	(144,378,000)	5,680,000	(20,245,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		15,484,000	15,484,000		$ 3,312,000	[1]	$ 12,172,000	[2]					12,172,000		3,312,000
Dividends declared and paid		(22,937,000)											(18,020,000)
Dividends declared and paid (noncontrolling interest)															(4,917,000)
Stock-based compensation		1,250,000										1,250,000
Other comprehensive loss - change in value of interest rate swaps																(6,115,000)	(6,115,000)	(6,115,000)	(4,816,000)	(1,299,000)
Reclassification of amortization of forward-starting swap included in interest expense		333,000	333,000	333,000										261,000	72,000
Ending Balance (shares) at Mar. 31, 2020									60,068,228
Ending Balance at Mar. 31, 2020		1,281,021,000							$ 601,000			1,453,264,000	(150,226,000)	603,000	(23,221,000)
Beginning partners' capital account (shares) at Dec. 31, 2019					16,390,548		60,068,228
Beginning partners' capital account at Dec. 31, 2019			1,293,672,000	7,716,000	$ (22,281,000)		$ 1,308,237,000
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		15,484,000	15,484,000		3,312,000	[1]	12,172,000	[2]					12,172,000		3,312,000
Distributions			(22,937,000)		$ (4,917,000)	[1]	(18,020,000)	[2]
Stock-based compensation			1,250,000				$ 1,250,000	[2]
Other comprehensive loss - change in value of interest rate swaps																(6,115,000)	(6,115,000)	(6,115,000)	(4,816,000)	(1,299,000)
Reclassification of amortization of forward-starting swap included in interest expense		333,000	333,000	333,000										261,000	72,000
Ending partners' capital account (shares) at Mar. 31, 2020					16,390,548		60,068,228
Ending partners' capital account at Mar. 31, 2020			1,281,021,000	1,268,000	$ (23,886,000)		$ 1,303,639,000
Beginning Balance (shares) at Dec. 31, 2019									60,068,228
Beginning Balance at Dec. 31, 2019		1,293,672,000							$ 601,000			1,452,014,000	(144,378,000)	5,680,000	(20,245,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		25,310,000	25,310,000
Conversion of operating partnership units (in shares)										0
Reclassification of amortization of forward-starting swap included in interest expense		665,000	665,000
Ending Balance (shares) at Jun. 30, 2020									60,073,918
Ending Balance at Jun. 30, 2020		1,276,488,000							$ 601,000			1,454,516,000	(154,516,000)	352,000	(24,465,000)
Beginning partners' capital account (shares) at Dec. 31, 2019					16,390,548		60,068,228
Beginning partners' capital account at Dec. 31, 2019			1,293,672,000	7,716,000	$ (22,281,000)		$ 1,308,237,000
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		25,310,000	25,310,000
Reclassification of amortization of forward-starting swap included in interest expense		665,000	665,000
Ending partners' capital account (shares) at Jun. 30, 2020					16,390,548		60,073,918
Ending partners' capital account at Jun. 30, 2020			1,276,488,000	950,000	$ (25,063,000)		$ 1,300,601,000
Beginning Balance (shares) at Mar. 31, 2020									60,068,228
Beginning Balance at Mar. 31, 2020		1,281,021,000							$ 601,000			1,453,264,000	(150,226,000)	603,000	(23,221,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		9,826,000	9,826,000		$ 2,101,000		$ 7,725,000						7,725,000		2,101,000
Issuance of restricted stock (shares)									6,008
Forfeiture of restricted stock (shares)									(318)
Dividends declared and paid		(15,293,000)											(12,015,000)
Dividends declared and paid (noncontrolling interest)															(3,278,000)
Stock-based compensation		1,252,000										1,252,000
Other comprehensive loss - change in value of interest rate swaps																14,000	14,000	14,000	10,000	4,000
Reclassification of amortization of forward-starting swap included in interest expense		332,000	332,000	332,000										261,000	71,000
Ending Balance (shares) at Jun. 30, 2020									60,073,918
Ending Balance at Jun. 30, 2020		1,276,488,000							$ 601,000			$ 1,454,516,000	(154,516,000)	352,000	(24,465,000)
Beginning partners' capital account (shares) at Mar. 31, 2020					16,390,548		60,068,228
Beginning partners' capital account at Mar. 31, 2020			1,281,021,000	1,268,000	$ (23,886,000)		$ 1,303,639,000
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		9,826,000	9,826,000		2,101,000		7,725,000						$ 7,725,000		2,101,000
Issuance of restricted units							$ 6,008
Forfeiture of restricted units							(318)
Distributions			(15,293,000)		$ (3,278,000)		$ (12,015,000)
Stock-based compensation			1,252,000				$ 1,252,000
Other comprehensive loss - change in value of interest rate swaps																$ 14,000	$ 14,000	$ 14,000	$ 10,000	$ 4,000
Reclassification of amortization of forward-starting swap included in interest expense		$ 332,000	332,000	332,000										$ 261,000	$ 71,000
Ending partners' capital account (shares) at Jun. 30, 2020					16,390,548		60,073,918
Ending partners' capital account at Jun. 30, 2020			$ 1,276,488,000	$ 950,000	$ (25,063,000)		$ 1,300,601,000

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

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