Consolidated Statement of Equity (Unaudited) - 9 months ended Sep. 30, 2018 - 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	[1]	American Assets Trust, L.P. General Partner		Common Shares	Common Shares American Assets Trust, L.P.	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 (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		17,993	$ 17,993		$ 4,765		$ 13,228	[2]				13,228		4,765
Issuance of restricted stock (in shares)									5,320
Issuance of restricted shares									$ 0		0
Forfeiture of restricted stock (in shares)									(5,000)
Forfeiture of restricted stock									$ 0		0
Conversion of operating partnership units (in shares)									17,372	17,372
Conversion of operating partnership units									$ 0		(916)			916
Dividends declared and paid		(52,164)										(38,241)
Dividends declared and paid (noncontrolling interest)														(13,923)
Stock-based compensation		2,180									2,180
Shares withheld for employee taxes (in shares)							(159)	[2]	(159)
Shares withheld for employee taxes		(6)	(6)				$ (6)	[2]	$ 0		(6)
Other comprehensive income - change in value of interest rate swaps		4,303	4,303												$ 4,303	$ 4,303	$ 4,303	$ 3,166	$ 1,137
Reclassification of amortization of forward-starting swap included in interest expense		(959)	(959)	$ (959)									(702)	(257)
Ending Balance (in shares) at Sep. 30, 2018									47,222,121
Ending Balance at Sep. 30, 2018		815,491							$ 473		920,324	(122,293)	13,915	3,072
Beginning partners' capital account (in shares) at Dec. 31, 2017					17,194,980		47,204,588	[2]
Beginning partners' capital account at Dec. 31, 2017			844,144	15,750	$ 6,135		$ 822,259	[2]
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		17,993	17,993		$ 4,765		$ 13,228	[2]				$ 13,228		4,765
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]						5,320
Forfeiture of restricted units (in shares)	[2]						(5,000)
Distributions			(52,164)		$ (13,923)		$ (38,241)	[2]
Stock-based compensation			2,180				$ 2,180	[2]
Shares withheld for employee taxes (in shares)							(159)	[2]	(159)
Shares withheld for employee taxes		(6)	(6)				$ (6)	[2]	$ 0		$ (6)
Other comprehensive income (loss) - unrealized income (loss) on swap derivative during the period		4,303	4,303												$ 4,303	$ 4,303	$ 4,303	$ 3,166	$ 1,137
Reclassification of amortization of forward-starting swap included in interest expense		$ (959)	(959)	(959)									$ (702)	$ (257)
Ending partners' capital account (in shares) at Sep. 30, 2018					17,177,608		47,222,121	[2]
Ending partners' capital account at Sep. 30, 2018			$ 815,491	$ 19,094	$ (2,107)		$ 798,504	[2]

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

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