Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
REVENUE:
Rental income		$ 330,312	$ 343,865	$ 309,537
Other property income		14,261	22,876	21,330
Total revenue		344,573	366,741	330,867
EXPENSES:
Rental expenses		79,178	91,967	86,482
Real estate taxes		41,941	40,013	34,973
General and administrative		26,581	24,871	22,784
Depreciation and amortization		108,292	96,205	107,093
Total operating expenses		255,992	253,056	251,332
Operating income (loss)		88,581	113,685	79,535
Interest expense		(53,440)	(54,008)	(52,248)
Gain on sale of real estate		0	633	0
Other income (expense), net		447	(122)	(85)
Net income		35,588	60,188	27,202
Net income attributable to restricted shares		(383)	(381)	(311)
Net income attributable to unitholders in the Operating Partnership		(7,545)	(14,089)	(7,205)
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST, INC. STOCKHOLDERS		$ 27,660	$ 45,718	$ 19,686
EARNINGS PER COMMON SHARE, BASIC
Basic net income attributable to common stockholders per share (in dollars per share)		$ 0.46	$ 0.84	$ 0.42
Weighted average shares of common stock outstanding-basic (in shares)		59,806,309	54,110,949	46,950,812
EARNINGS PER COMMON SHARE, DILUTED
Diluted net income attributable to common stockholders per share (in dollars per share)		$ 0.46	$ 0.84	$ 0.42
Weighted average shares of common stock outstanding-diluted (in shares)		76,119,763	70,786,132	64,136,559
COMPREHENSIVE INCOME
Net income		$ 35,588	$ 60,188	$ 27,202
Other comprehensive (loss) gain - unrealized (loss) gain on swap derivatives during the period		(3,649)	(5,571)	120
Reclassification of amortization of forward starting swaps included in interest expense		(1,330)	(1,304)	(1,279)
Comprehensive income		30,609	53,313	26,043
Comprehensive income attributable to noncontrolling interest		(6,496)	(12,301)	(6,877)
Comprehensive income attributable to American Assets Trust, Inc.		24,113	41,012	19,166
American Assets Trust, L.P.
REVENUE:
Rental income		330,312	343,865	309,537
Other property income		14,261	22,876	21,330
Total revenue		344,573	366,741	330,867
EXPENSES:
Rental expenses		79,178	91,967	86,482
Real estate taxes		41,941	40,013	34,973
General and administrative		26,581	24,871	22,784
Depreciation and amortization		108,292	96,205	107,093
Total operating expenses		255,992	253,056	251,332
Operating income (loss)		88,581	113,685	79,535
Interest expense		(53,440)	(54,008)	(52,248)
Gain on sale of real estate		0	633	0
Other income (expense), net		447	(122)	(85)
Net income		35,588	60,188	27,202
Net income attributable to restricted shares		(383)	(381)	(311)
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST, INC. STOCKHOLDERS		$ 35,205	$ 59,807	$ 26,891
EARNINGS PER COMMON SHARE, BASIC
Basic net income attributable to common stockholders per share (in dollars per share)		$ 0.46	$ 0.84	$ 0.42
Weighted average shares of common stock outstanding-basic (in shares)		76,119,763	70,786,132	64,136,559
EARNINGS PER COMMON SHARE, DILUTED
Diluted net income attributable to common stockholders per share (in dollars per share)		$ 0.46	$ 0.84	$ 0.42
Weighted average shares of common stock outstanding-diluted (in shares)		76,119,763	70,786,132	64,136,559
DISTRIBUTIONS PER UNIT (in dollars per share)		$ 1.00	$ 1.14	$ 1.09
COMPREHENSIVE INCOME
Net income		$ 35,588	$ 60,188	$ 27,202
Reclassification of amortization of forward starting swaps included in interest expense		(1,330)	(1,304)	(1,279)
Comprehensive income		30,609	53,313	26,043
American Assets Trust, L.P. | Limited Partner
EXPENSES:
Net income	[1]	7,545	14,089	7,205
COMPREHENSIVE INCOME
Net income	[1]	7,545	14,089	7,205
Comprehensive income attributable to American Assets Trust, Inc.		(6,496)	(12,301)	(6,877)
American Assets Trust, L.P. | General Partner
EXPENSES:
Net income	[2]	28,043	46,099	19,997
COMPREHENSIVE INCOME
Net income	[2]	28,043	46,099	19,997
Comprehensive income attributable to American Assets Trust, Inc.		24,113	41,012	19,166
Interest Rate Swap | American Assets Trust, L.P.
COMPREHENSIVE INCOME
Other comprehensive (loss) gain - unrealized (loss) gain on swap derivatives during the period		(3,649)	(5,571)	120
Swap
COMPREHENSIVE INCOME
Other comprehensive (loss) gain - unrealized (loss) gain on swap derivatives during the period		(3,649)	(6,084)	120
Swap | American Assets Trust, L.P.
COMPREHENSIVE INCOME
Other comprehensive (loss) gain - unrealized (loss) gain on swap derivatives during the period		$ (3,649)	(6,084)	$ 120
Forward Contracts
COMPREHENSIVE INCOME
Other comprehensive (loss) gain - unrealized (loss) gain on swap derivatives during the period			513
Forward Contracts | American Assets Trust, L.P.
COMPREHENSIVE INCOME
Other comprehensive (loss) gain - unrealized (loss) gain on swap derivatives during the period			$ 513

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

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