Intangible Assets (Components of Intangible Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 99,063	$ 53,483
Goodwill	1,674	1,674	$ 3,626	$ 3,647
Total intangible assets	211,786	245,529
In-place Leases
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	158,395	185,251
Accumulated amortization	85,806	46,899
Above-market Tenant Leases
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	33,580	40,260
Accumulated amortization	12,981	6,515
Below-market Ground Lease
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	18,137	18,344
Accumulated amortization	$ 276	$ 69