REAL ESTATE (Details) ft² in Thousands, $ in Thousands			3 Months Ended							9 Months Ended
	Jun. 20, 2019 USD ($) ft²	May 22, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 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			$ 32,837	$ 32,837						32,837		$ 6,281
Prepaid expenses and other			6,683	6,683						6,683		6,683
Assets			2,788,958	2,788,958						2,788,958		2,198,250
Accounts payable and accrued expenses			63,205	63,205						63,205		46,616
Security deposits payable			7,855	7,855						7,855		8,844
Other liabilities and deferred credits, net			61,990	61,990						61,990		49,547
Liabilities			1,490,734	1,490,734						$ 1,490,734		1,395,779
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life										8 years 4 months 24 days
Revenues			98,362				$ 82,507			$ 267,794	248,262
Operating Expenses			67,978				55,232			184,102	190,818
Operating Income (Loss)			30,384				27,275			83,692	57,444
Net income			16,519		$ 11,941	$ 15,243	14,271	$ 4,413	$ (691)	43,703	17,993
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				10,615
Operating Expenses				10,118
Operating Income (Loss)				497
Net income				497
Pro Forma
Real Estate [Line Items]
Revenues										283,676	276,129
Operating Expenses										195,645	213,513
Operating Income (Loss)										88,031	62,616
Net income										47,110	22,356
American Assets Trust, L.P.
Real Estate [Line Items]
Proceeds from sale of real estate, net of selling costs										8,191	0
Assets			2,788,958	2,788,958						2,788,958		2,198,250
Accounts payable and accrued expenses			63,205	63,205						63,205		46,616
Security deposits payable			7,855	7,855						7,855		8,844
Other liabilities and deferred credits, net			61,990	61,990						61,990		49,547
Liabilities			1,490,734	$ 1,490,734						1,490,734		$ 1,395,779
Revenues			98,362				82,507			267,794	248,262
Operating Expenses			67,978				55,232			184,102	190,818
Operating Income (Loss)			30,384				27,275			83,692	57,444
Net income			$ 16,519		$ 11,941	$ 15,243	$ 14,271	$ 4,413	$ (691)	$ 43,703	$ 17,993