Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Intangible Assets [Line Items]
Intangible Assets, Total Cost	$ 196,417	$ 123,806
Intangible Assets, Accumulated Amortization	(65,069)	(58,834)
Intangible Assets, net	131,348	64,972
Acquired Lease Intangibles, Net	31,783	20,274
Below market leases [Member]
Intangible Assets [Line Items]
Acquired Lease Intangibles, Gross	49,655	36,213
Acquired Lease Intangibles, Accumulated Amortization	(17,872)	(15,939)
Acquired Lease Intangibles, Net	31,783	20,274
In-place lease value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	181,887	108,060
Intangible Assets, Accumulated Amortization	(53,376)	(47,003)
Intangible Assets, net	128,511	61,057
Tenant relationship value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	9,564	11,201
Intangible Assets, Accumulated Amortization	(8,551)	(9,275)
Intangible Assets, net	1,013	1,926
Above market leases acquired [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	4,966	4,545
Intangible Assets, Accumulated Amortization	(3,142)	(2,556)
Intangible Assets, net	$ 1,824	$ 1,989