Consolidated Statements of Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Accumulated dividends in excess of net income	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests - Unitholders in the Operating Partnership	American Assets Trust, L.P.	Swap	Swap Accumulated Other Comprehensive Income (Loss)	Swap Noncontrolling Interests - Unitholders in the Operating Partnership	Swap American Assets Trust, L.P.	Forward Contracts	Forward Contracts Accumulated Other Comprehensive Income (Loss)	Forward Contracts Noncontrolling Interests - Unitholders in the Operating Partnership	Forward Contracts American Assets Trust, L.P.	Limited Partner American Assets Trust, L.P.	General Partner American Assets Trust, L.P.	Accumulated Other Comprehensive Income (Loss) American Assets Trust, L.P.	Accumulated Other Comprehensive Income (Loss) Swap American Assets Trust, L.P.	Accumulated Other Comprehensive Income (Loss) Forward Contracts American Assets Trust, L.P.
Partners' Capital at Dec. 31, 2011							$ 679,728									$ 53,697	$ 626,031	$ 0
Beginning Balance at Dec. 31, 2011	679,728	393	653,645	(28,007)	0	53,697
Partners' Capital Account, Units at Dec. 31, 2011																18,396,089	39,283,796
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	51,601			35,467		16,134	51,601									16,134	35,467
Conversion of operating partnership units (in shares)		372,654
Conversion of operating partnership units		4	7,092			(7,096)
Issuance of restricted stock (in shares)		10,015
Forfeiture of restricted stock (in shares)		(2,253)
Dividends declared and paid	(48,452)			(33,085)		(15,367)
Stock-based compensation	2,852		2,852
Other comprehensive income (loss) unrealized gain (loss) on derivatives								0				0
Reclassification of amortization of forward starting swap included in interest expense	0						0
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	51,601			35,467		16,134	51,601									16,134	35,467
Conversion of operating partnership units (in shares)																(372,654)	372,654
Conversion of operating partnership units																(7,096)	7,096
Issuance of restricted units (in shares)																	10,015
Forfeiture of restricted units																	(2,253)
Distributions							(48,452)									(15,367)	(33,085)
Stock-based compensation							2,852										2,852
Shares, Outstanding		39,664,212
Partners' Capital at Dec. 31, 2012							685,729									47,368	638,361	0
Ending Balance at Dec. 31, 2012	685,729	397	663,589	(25,625)	0	47,368
Partners' Capital Account, Units at Dec. 31, 2012																18,023,435	39,664,212
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,865						4,865
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	4,865						4,865
Partners' Capital at Mar. 31, 2013
Partners' Capital at Dec. 31, 2012							685,729									47,368	638,361	0
Beginning Balance at Dec. 31, 2012	685,729	397	663,589	(25,625)	0	47,368
Partners' Capital Account, Units at Dec. 31, 2012																18,023,435	39,664,212
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	22,594			15,756		6,838	22,594									6,838	15,756
Common shares issued (in shares)		741,452
Common shares issued	24,910	7	24,903
Conversion of operating partnership units (in shares)		106,326
Conversion of operating partnership units	0	1	859			(860)
Issuance of restricted stock (in shares)		5,004
Issuance of restricted stock	0	0
Forfeiture of restricted stock (in shares)		(4,431)
Forfeiture of restricted stock	0	0
Dividends declared and paid	(49,500)			(34,221)		(15,279)
Stock-based compensation	2,845		2,845
Other comprehensive income (loss) unrealized gain (loss) on derivatives								0				0
Reclassification of amortization of forward starting swap included in interest expense	0						0
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	22,594			15,756		6,838	22,594									6,838	15,756
Conversion of operating partnership units (in shares)																(106,326)	106,326
Conversion of operating partnership units																(860)	860
Issuance of restricted units (in shares)																	5,004
Forfeiture of restricted units																	(4,431)
Distributions							(49,500)									(15,279)	(34,221)
Stock-based compensation							2,845										2,845
Contributions from American Assets Trust, Inc. (in shares)																	741,452
Contributions from American Assets Trust, Inc.							24,910										24,910
Shares, Outstanding		40,512,563
Partners' Capital at Dec. 31, 2013							686,578									38,067	648,511
Ending Balance at Dec. 31, 2013	686,578	405	692,196	(44,090)		38,067
Partners' Capital Account, Units at Dec. 31, 2013																17,917,109	40,512,563
Ending Balance (in shares) at Dec. 31, 2013	40,512,563
Partners' Capital at Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,907						6,907
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	6,907						6,907
Partners' Capital at Dec. 31, 2013							686,578
Ending Balance at Dec. 31, 2013	686,578
Ending Balance (in shares) at Dec. 31, 2013	40,512,563
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,658						6,658
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	6,658						6,658
Partners' Capital at Mar. 31, 2014
Partners' Capital at Dec. 31, 2013							686,578									38,067	648,511	0
Beginning Balance at Dec. 31, 2013	686,578	405	692,196	(44,090)	0	38,067
Partners' Capital Account, Units at Dec. 31, 2013																17,917,109	40,512,563
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31,145			22,130		9,015	31,145									9,015	22,130
Common shares issued (in shares)		3,110,067
Common shares issued	104,148	31	104,117
Conversion of operating partnership units (in shares)		11,852
Conversion of operating partnership units			(133)			133
Issuance of restricted stock (in shares)		216,748
Issuance of restricted stock	0	2	(2)
Forfeiture of restricted stock (in shares)		(1,192)
Forfeiture of restricted stock	0	0
Dividends declared and paid	(54,311)			(38,331)		(15,980)
Stock-based compensation	3,666		3,666
Shares withheld for employee taxes (in shares)		(148,369)															148,369
Shares withheld for employee taxes	(4,780)	(1)	(4,779)				4,780										4,780
Other comprehensive income (loss) unrealized gain (loss) on derivatives								(1,448)	(1,024)	(424)	(1,448)	1,617	1,144	473	1,617				(1,448)	1,617
Reclassification of amortization of forward starting swap included in interest expense	(39)				(28)	(11)	(39)
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	31,145			22,130		9,015	31,145									9,015	22,130
Conversion of operating partnership units (in shares)																(11,852)	11,852
Conversion of operating partnership units																133	(133)
Issuance of restricted units (in shares)																	216,748
Forfeiture of restricted units																	(1,192)
Distributions							(54,311)									(15,980)	(38,331)
Stock-based compensation							3,666										3,666
Contributions from American Assets Trust, Inc. (in shares)																	3,110,067
Contributions from American Assets Trust, Inc.							104,148										104,148
Reclassification of amortization of forward starting swap included in interest expense							(39)											(39)
Shares, Outstanding		43,701,669
Partners' Capital at Dec. 31, 2014							766,576									31,235	735,211	130
Ending Balance at Dec. 31, 2014	766,576	437	795,065	(60,291)	92	31,273
Partners' Capital Account, Units at Dec. 31, 2014																17,905,257	43,701,669
Ending Balance (in shares) at Dec. 31, 2014	43,701,669
Partners' Capital at Sep. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	10,046						10,046
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	10,046						10,046
Partners' Capital at Dec. 31, 2014							766,576
Ending Balance at Dec. 31, 2014	$ 766,576
Ending Balance (in shares) at Dec. 31, 2014	43,701,669