Consolidated Statements of Income (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
REVENUE:
Rental income	$ 246,078	$ 242,757	$ 225,249
Other property income	13,922us-gaap_OtherRealEstateRevenue	12,300us-gaap_OtherRealEstateRevenue	10,217us-gaap_OtherRealEstateRevenue
Total revenue	260,000us-gaap_Revenues	255,057us-gaap_Revenues	235,466us-gaap_Revenues
EXPENSES:
Rental expenses	68,267us-gaap_CostOfRealEstateRevenue	68,608us-gaap_CostOfRealEstateRevenue	64,089us-gaap_CostOfRealEstateRevenue
Real estate taxes	22,964us-gaap_RealEstateTaxExpense	21,378us-gaap_RealEstateTaxExpense	22,025us-gaap_RealEstateTaxExpense
General and administrative	18,532us-gaap_GeneralAndAdministrativeExpense	17,195us-gaap_GeneralAndAdministrativeExpense	15,593us-gaap_GeneralAndAdministrativeExpense
Depreciation and amortization	66,568us-gaap_DepreciationAndAmortization	66,775us-gaap_DepreciationAndAmortization	61,853us-gaap_DepreciationAndAmortization
Total operating expenses	176,331us-gaap_OperatingExpenses	173,956us-gaap_OperatingExpenses	163,560us-gaap_OperatingExpenses
Operating income (loss)	83,669us-gaap_OperatingIncomeLoss	81,101us-gaap_OperatingIncomeLoss	71,906us-gaap_OperatingIncomeLoss
Interest expense	(52,965)	(58,020)	(57,328)
Other income (expense), net	441us-gaap_OtherNonoperatingIncomeExpense	(487)us-gaap_OtherNonoperatingIncomeExpense	(629)us-gaap_OtherNonoperatingIncomeExpense
INCOME FROM CONTINUING OPERATIONS	31,145	22,594	13,949
Discontinued operations
Income from discontinued operations	0	0	932
Gain on sale of real estate property	0	0	36,720
Results from discontinued operations	0	0	37,652
NET INCOME	31,145us-gaap_ProfitLoss	22,594us-gaap_ProfitLoss	51,601us-gaap_ProfitLoss
Net income attributable to restricted shares	(374)	(536)	(529)
Net income attributable to unitholders in the Operating Partnership	(9,015)	(6,838)	(16,134)
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST, INC. STOCKHOLDERS	21,756us-gaap_NetIncomeLoss	15,220us-gaap_NetIncomeLoss	34,938us-gaap_NetIncomeLoss
EARNINGS PER COMMON SHARE, BASIC
Continuing operations (in dollars per share)	$ 0.52	$ 0.38	$ 0.24
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00	$ 0.66
Basic net income attributable to common stockholders per share (in dollars per share)	$ 0.52us-gaap_EarningsPerShareBasic	$ 0.38us-gaap_EarningsPerShareBasic	$ 0.90us-gaap_EarningsPerShareBasic
Weighted average shares of common stock outstanding-basic (in shares)	42,041,126	39,539,457	38,736,113
EARNINGS PER COMMON SHARE, DILUTED
Continuing operations (in dollars per share)	$ 0.51	$ 0.38	$ 0.24
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00	$ 0.66
Diluted net income attributable to common stockholders per share (in dollars per share)	$ 0.51us-gaap_EarningsPerShareDiluted	$ 0.38us-gaap_EarningsPerShareDiluted	$ 0.90us-gaap_EarningsPerShareDiluted
Weighted average shares of common stock outstanding-diluted (in shares)	59,947,474	57,515,810	57,053,909
COMPREHENSIVE INCOME
Net income	31,145us-gaap_ProfitLoss	22,594us-gaap_ProfitLoss	51,601us-gaap_ProfitLoss
Reclassification of amortization of forward starting swap included in interest expense	(39)	0	0
Comprehensive income	31,275	22,594	51,601
Comprehensive income attributable to non-controlling interest	(9,053)	(6,838)	(16,134)
Comprehensive income attributable to American Assets Trust, Inc.	22,222us-gaap_ComprehensiveIncomeNetOfTax	15,756us-gaap_ComprehensiveIncomeNetOfTax	35,467us-gaap_ComprehensiveIncomeNetOfTax
American Assets Trust, L.P.
REVENUE:
Rental income	246,078	242,757	225,249
Other property income	13,922	12,300	10,217
Total revenue	260,000	255,057	235,466
EXPENSES:
Rental expenses	68,267	68,608	64,089
Real estate taxes	22,964	21,378	22,025
General and administrative	18,532	17,195	15,593
Depreciation and amortization	66,568	66,775	61,853
Total operating expenses	176,331	173,956	163,560
Operating income (loss)	83,669	81,101	71,906
Interest expense	(52,965)	(58,020)	(57,328)
Other income (expense), net	441	(487)	(629)
INCOME FROM CONTINUING OPERATIONS	31,145	22,594	13,949
Discontinued operations
Income from discontinued operations	0	0	932
Gain on sale of real estate property	0	0	36,720
Results from discontinued operations	0	0	37,652
NET INCOME	31,145	22,594	51,601
Net income attributable to restricted shares	(374)	(536)	(529)
Net income attributable to unitholders in the Operating Partnership	(9,015)	(6,838)	(16,134)
NET INCOME ATTRIBUTABLE TO AMERICAN ASSETS TRUST, INC. STOCKHOLDERS	21,756	15,220	34,938
EARNINGS PER COMMON SHARE, BASIC
Continuing operations (in dollars per share)	$ 0.52	$ 0.38	$ 0.24
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00	$ 0.66
Basic net income attributable to common stockholders per share (in dollars per share)	$ 0.52	$ 0.38	$ 0.90
Weighted average shares of common stock outstanding-basic (in shares)	42,041,126	39,539,457	38,736,113
EARNINGS PER COMMON SHARE, DILUTED
Continuing operations (in dollars per share)	$ 0.51	$ 0.38	$ 0.24
Discontinued operations (in dollars per share)	$ 0.00	$ 0.00	$ 0.66
Diluted net income attributable to common stockholders per share (in dollars per share)	$ 0.51	$ 0.38	$ 0.90
Weighted average shares of common stock outstanding-diluted (in shares)	59,947,474	57,515,810	57,053,909
DISTRIBUTIONS PER UNIT	$ 0.8925	$ 0.85	$ 0.84
COMPREHENSIVE INCOME
Net income	31,145	22,594	51,601
Reclassification of amortization of forward starting swap included in interest expense	(39)	0	0
Comprehensive income	31,275	22,594	51,601
Limited Partner \| American Assets Trust, L.P.
Discontinued operations
NET INCOME	9,015	6,838	16,134
COMPREHENSIVE INCOME
Net income	9,015	6,838	16,134
Comprehensive income attributable to American Assets Trust, Inc.	(9,053)	(6,838)	(16,134)
General Partner \| American Assets Trust, L.P.
Discontinued operations
NET INCOME	22,130	15,756	35,467
COMPREHENSIVE INCOME
Net income	22,130	15,756	35,467
Comprehensive income attributable to American Assets Trust, Inc.	22,222	15,756	35,467
Swap
COMPREHENSIVE INCOME
Other comprehensive loss - unrealized loss on swap derivative during the period	(1,448)	0	0
Swap \| American Assets Trust, L.P.
COMPREHENSIVE INCOME
Other comprehensive loss - unrealized loss on swap derivative during the period	(1,448)
Forward Contracts
COMPREHENSIVE INCOME
Other comprehensive loss - unrealized loss on swap derivative during the period	1,617	0	0
Forward Contracts \| American Assets Trust, L.P.
COMPREHENSIVE INCOME
Other comprehensive loss - unrealized loss on swap derivative during the period	$ 1,617

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