REAL ESTATE (Details) ft² in Thousands, $ in Thousands				3 Months Ended				6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 20, 2019 USD ($) ft²	May 22, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Real Estate [Line Items]
Proceeds from sale of real estate, net of selling costs								$ 8,191	$ 0
Acquired in-place leases, net	$ 34,657			$ 34,657				34,657		$ 6,281
Prepaid expenses and other	5,388			5,388				5,388		6,683
Assets	2,718,758			2,718,758				2,718,758		2,198,250
Accounts payable and accrued expenses	54,652			54,652				54,652		46,616
Security deposits payable	7,907			7,907				7,907		8,844
Other liabilities and deferred credits, net	62,362			62,362				62,362		49,547
Liabilities	1,426,836			1,426,836				$ 1,426,836		1,395,779
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life								8 years 8 months 12 days
Revenues				84,113		$ 85,023		$ 169,432	165,755
Operating Expenses				59,626		67,774		116,124	135,586
Operating Income (Loss)				24,487		17,249		53,308	30,169
Net income				11,941	$ 15,243	4,413	$ (691)	27,184	3,722
Solana Beach Highway One Zero One
Real Estate [Line Items]
Sales Price of Property Sold			$ 9,400
Proceeds from sale of real estate, net of selling costs			$ 9,400
Gains (Losses) on Sales of Investment Real Estate								600
La Jolla Commons
Real Estate [Line Items]
Payments to Acquire Productive Assets		$ 525,000
Purchase Price Seller Credits - Speculative Leasing		11,500
Purchase Price Seller Credits - Assumed Contractual Liabilities		4,200
Purchase Price Seller Credits - Closing Prorations		1,700
Acquisition Cost Capitalized		$ 200
Area of Real Estate Property | ft²		724
Land	82,759			82,759				82,759
Buildings and Improvements, Gross	361,471			361,471				361,471
Land Improvements	1,359			1,359				1,359
Furniture and Fixtures, Gross	30,822			30,822				30,822
Property, Plant and Equipment, Gross	476,411			476,411				476,411
Acquired in-place leases, net	40,082			40,082				40,082
Prepaid expenses and other	13			13				13
Assets	516,506			516,506				516,506
Accounts payable and accrued expenses	3,578			3,578				3,578
Security deposits payable	443			443				443
Other liabilities and deferred credits, net	3,817			3,817				3,817
Liabilities	7,838			7,838				7,838
Revenues	1,168
Operating Expenses	1,996
Operating Income (Loss)	(828)
Net income	(828)
Pro Forma
Real Estate [Line Items]
Revenues								185,876	184,359
Operating Expenses								128,236	150,861
Operating Income (Loss)								57,640	33,498
Net income								30,888	6,524
American Assets Trust, L.P.
Real Estate [Line Items]
Proceeds from sale of real estate, net of selling costs								8,191	0
Assets	2,718,758			2,718,758				2,718,758		2,198,250
Accounts payable and accrued expenses	54,652			54,652				54,652		46,616
Security deposits payable	7,907			7,907				7,907		8,844
Other liabilities and deferred credits, net	62,362			62,362				62,362		49,547
Liabilities	$ 1,426,836			1,426,836				1,426,836		$ 1,395,779
Revenues				84,113		85,023		169,432	165,755
Operating Expenses				59,626		67,774		116,124	135,586
Operating Income (Loss)				24,487		17,249		53,308	30,169
Net income				$ 11,941	$ 15,243	$ 4,413	$ (691)	$ 27,184	$ 3,722