Investments in Unconsolidated Joint Ventures (Kings Hill Unit Trust) (Details) - United Kingdom [Member] ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) ft² properties	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Kings Hill Unit Trust [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage	20.00%
Kings Hill Unit Trust [Member] | Equity Method Investee [Member]
Schedule of Equity Method Investments [Line Items]
Note receivable interest rate	10.00%
Management fees revenue	$ 293	$ 304	$ 285
Building and Building Improvements [Member] | Kings Hill Unit Trust [Member]
Schedule of Equity Method Investments [Line Items]
Leaseable square feet | ft²	490
Building and Building Improvements [Member] | Industrial Property [Member] | Kings Hill Unit Trust [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties | properties	3
Building and Building Improvements [Member] | Office Building [Member] | Kings Hill Unit Trust [Member]
Schedule of Equity Method Investments [Line Items]
Number of properties | properties	11
Investments in and advances to unconsolidated joint ventures [Member] | Kings Hill Unit Trust [Member] | Equity Method Investee [Member]
Schedule of Equity Method Investments [Line Items]
Notes receivable	$ 4,100	4,700
Prepaid Expenses and Other Current Assets [Member] | Kings Hill Unit Trust [Member] | Equity Method Investee [Member]
Schedule of Equity Method Investments [Line Items]
Due from related parties	$ 121	$ 271