Intangible Assets and Liabilities - Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Intangible Assets [Line Items]
Intangible Assets, Total Cost	$ 121,879	$ 123,806
Intangible Assets, Accumulated Amortization	(58,265)	(58,834)
Intangible Assets, net	63,614	64,972
Acquired Lease Intangibles, Net	19,510	20,274
Below market leases [Member]
Intangible Assets [Line Items]
Acquired Lease Intangibles, Gross	35,719	36,213
Acquired Lease Intangibles, Accumulated Amortization	(16,209)	(15,939)
Acquired Lease Intangibles, Net	19,510	20,274
In-place lease value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	106,574	108,060
Intangible Assets, Accumulated Amortization	(46,495)	(47,003)
Intangible Assets, net	60,079	61,057
Tenant relationship value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	10,593	11,201
Intangible Assets, Accumulated Amortization	(9,064)	(9,275)
Intangible Assets, net	1,529	1,926
Above market leases acquired [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	4,712	4,545
Intangible Assets, Accumulated Amortization	(2,706)	(2,556)
Intangible Assets, net	$ 2,006	$ 1,989