Intangibles - Acquired Lease Intangible Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
In-place leases
Finite-Lived Intangible Assets [Line Items]
Amortization expense related to in-place leases	$ 37,073	$ 28,902	$ 15,300
Above-market leases
Finite-Lived Intangible Assets [Line Items]
Decrease of rental income	5,357	4,403	2,596
Leasehold interest
Finite-Lived Intangible Assets [Line Items]
Decrease of rental income	59	59	59
Below-market lease
Finite-Lived Intangible Assets [Line Items]
Increase of rental income related to below-market leases	2,309	1,835	643
Below-market in-place ground lease
Finite-Lived Intangible Assets [Line Items]
Decrease (increase) of operating expense	84	24	16
Below-market ground lease
Finite-Lived Intangible Assets [Line Items]
Decrease (increase) of operating expense	$ 810	$ 471	$ 68