Consolidated Statements of Equity - USD ($) $ in Thousands	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.
Increase (Decrease) in Partners' Capital [Roll Forward]
Shares, Outstanding		39,283,796
Beginning Balance at Dec. 31, 2011	$ 679,728	$ 393	$ 653,645	$ (28,007)	$ 0	$ 53,697
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
Ending Balance at Dec. 31, 2012	685,729	$ 397	663,589	(25,625)	0	47,368
Partners' Capital Account, Units at Dec. 31, 2011																18,396,089	39,283,796
Partners' Capital at Dec. 31, 2011							679,728									$ 53,697	$ 626,031	$ 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
Other comprehensive income (loss) unrealized gain (loss) on derivatives								0				0
Partners' Capital at Dec. 31, 2012							685,729									$ 47,368	$ 638,361	0
Partners' Capital Account, Units at Dec. 31, 2012																18,023,435	39,664,212
Increase (Decrease) in Partners' Capital [Roll Forward]
Shares, Outstanding		39,664,212
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
Ending Balance at Dec. 31, 2013	$ 686,578	$ 405	692,196	(44,090)	0	38,067
Ending Balance (in shares) at Dec. 31, 2013	40,512,563
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
Other comprehensive income (loss) unrealized gain (loss) on derivatives								0				0
Partners' Capital at Dec. 31, 2013							686,578									$ 38,067	$ 648,511	0
Partners' Capital Account, Units at Dec. 31, 2013																17,917,109	40,512,563
Increase (Decrease) in Partners' Capital [Roll Forward]
Shares, Outstanding		40,512,563
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)
Ending Balance at Dec. 31, 2014	$ 766,576	$ 437	$ 795,065	(60,291)	$ 92	31,273
Ending Balance (in shares) at Dec. 31, 2014	43,701,669
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
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)											(39)
Partners' Capital at Dec. 31, 2014							$ 766,576									$ 31,235	$ 735,211	$ 130
Partners' Capital Account, Units at Dec. 31, 2014																17,905,257	43,701,669
Increase (Decrease) in Partners' Capital [Roll Forward]
Shares, Outstanding		43,701,669