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Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 01, 2017	Jul. 01, 2016	Jul. 01, 2015	Jul. 01, 2014
Related Party Transaction [Line Items]
Total rental income	$ 309,537	$ 298,803	$ 279,498
Investment in WBW CHP LLC, in percentage	47.70%
WBW CHP LLC
Related Party Transaction [Line Items]
Recovered reimbursements of operating expenses of WBW CHP LLC	$ 1,100	$ 1,000	$ 900
Common Stock
Related Party Transaction [Line Items]
Common shares issued (in shares)		700,000	219,480
Insurance Company of the West, Inc. \| Board of Directors Chairman
Related Party Transaction [Line Items]
Total rental income	$ 100	$ 100	$ 2,200
Prepaid insurance				$ 200	$ 200	$ 200	$ 400
Percentage of ownership interests classified as noncontrolling	37.00%
Insurance Company of the West, Inc. \| Common Stock \| Board of Directors Chairman
Related Party Transaction [Line Items]
Percentage of ownership interests classified as noncontrolling	14.00%
Insurance Company of the West, Inc. \| Member Units \| Board of Directors Chairman
Related Party Transaction [Line Items]
Percentage of ownership interests classified as noncontrolling	23.10%
American Assets, Inc. \| Board of Directors Chairman
Related Party Transaction [Line Items]
Total rental income	$ 100
EDisability, LLC \| Board of Directors Chairman
Related Party Transaction [Line Items]
Total rental income	100
AAI Aviation, Inc. \| Board of Directors Chairman
Related Party Transaction [Line Items]
Aviation expense	$ 100	$ 100	$ 200