Intangible Assets and Liabilities - Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Intangible Assets [Line Items]
Intangible Assets, Total Cost	$ 117,704	$ 160,681
Intangible Assets, Accumulated Amortization	(58,887)	(88,203)
Intangible Assets, net	58,817	72,478
Acquired Lease Intangibles, Net	17,156	18,119
Below market leases [Member]
Intangible Assets [Line Items]
Acquired Lease Intangibles, Gross	32,158	37,579
Acquired Lease Intangibles, Accumulated Amortization	(15,002)	(19,460)
Acquired Lease Intangibles, Net	17,156	18,119
In-place lease value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	100,519	142,889
Intangible Assets, Accumulated Amortization	(45,765)	(75,696)
Intangible Assets, net	54,754	67,193
Tenant relationship value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	12,831	13,074
Intangible Assets, Accumulated Amortization	(10,646)	(10,167)
Intangible Assets, net	2,185	2,907
Above market leases acquired [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	4,354	4,718
Intangible Assets, Accumulated Amortization	(2,476)	(2,340)
Intangible Assets, net	$ 1,878	$ 2,378