Derivative and Hedging (Details) - USD ($)											12 Months Ended
	Mar. 31, 2017	Jan. 18, 2017	May 02, 2016	Apr. 07, 2016	Mar. 29, 2016	Mar. 23, 2016	Mar. 01, 2016	Jan. 29, 2016	Sep. 19, 2014	Aug. 19, 2014	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative liabilities at fair value											$ (1,067,000)	$ (1,686,000)
Derivative assets at fair value											$ 16,428,000	$ 0
Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount				$ 100,000,000	$ 150,000,000
Fixed interest rate on derivative				1.748%	1.88%
American Assets Trust, L.P. | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount										$ 150,000,000
Fixed interest rate on derivative										2.1305%	3.08%
Term of derivative contract				10 years	10 years					7 years	7 years
American Assets Trust, L.P. | Forward Contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Term of derivative contract										1 month	1 month
American Assets Trust, L.P. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount						$ 50,000,000		$ 100,000,000			$ 100,000,000
Fixed interest rate on derivative						1.441%		1.4485%			3.08%
Term of derivative contract						7 years		7 years
Maturity date				Mar. 31, 2027	Mar. 31, 2027	Mar. 01, 2023		Mar. 01, 2023
Effective date				Mar. 31, 2017	Mar. 31, 2017	May 02, 2016		Mar. 01, 2016
Gain recognized in other comprehensive income (loss)									$ 1,600,000
American Assets Trust, L.P. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 1/9/2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Maturity date											Jan. 09, 2019
Effective date											Jan. 09, 2014
Bank of America, N.A. | American Assets Trust, L.P. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 1/9/2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount											$ 100,000,000
Derivative liabilities at fair value											$ (1,067,000)
U.S. Bank N.A. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 3/1/2023
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Maturity date											Mar. 01, 2023
U.S. Bank N.A. | American Assets Trust, L.P. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 3/1/2023
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount											$ 100,000,000
Effective date											Mar. 01, 2016
Derivative assets at fair value											$ 2,751,000
Wells Fargo Bank, N.A. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 3/1/2023
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Maturity date											Mar. 01, 2023
Wells Fargo Bank, N.A. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 3/31/2027 $150M
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Maturity date											Mar. 31, 2027
Wells Fargo Bank, N.A. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 3/31/2027 $100M
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Maturity date											Mar. 31, 2027
Wells Fargo Bank, N.A. | American Assets Trust, L.P. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 3/1/2023
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount											$ 50,000,000
Effective date											May 02, 2016
Derivative assets at fair value											$ 1,414,000
Wells Fargo Bank, N.A. | American Assets Trust, L.P. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 3/31/2027 $150M
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount					$ 150,000,000						$ 150,000,000
Effective date											Mar. 31, 2017
Derivative assets at fair value											$ 6,638,000
Wells Fargo Bank, N.A. | American Assets Trust, L.P. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap, 3/31/2027 $100M
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount				$ 100,000,000							$ 100,000,000
Effective date											Mar. 31, 2017
Derivative assets at fair value											$ 5,625,000
Term Loan B | American Assets Trust, L.P.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Stated Maturity Date							Mar. 01, 2023	Mar. 01, 2023
Face amount of debt							$ 100,000,000
Number of year amortization schedule							7 years
Term Loan B | American Assets Trust, L.P. | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fixed interest rate on derivative											3.15%
Term Loan C | American Assets Trust, L.P.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Stated Maturity Date			Mar. 01, 2023			Mar. 01, 2023
Face amount of debt			$ 50,000,000
Number of year amortization schedule			7 years
Term Loan C | American Assets Trust, L.P. | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fixed interest rate on derivative											3.14%
Scenario, Forecast | Unsecured debt | American Assets Trust, L.P.
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of year amortization schedule	10 years
Subsequent Event | American Assets Trust, L.P. | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain recognized in other comprehensive income (loss)		$ 10,400,000