Lease Intangibles - Schedule of Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortizable Intangible Assets, Gross Carrying Amount	$ 217,106	$ 210,607
Amortizable Intangible Assets, Accumulated Amortization	(92,056)	(83,036)
Amortizable Intangible Assets, Net Carrying Amount	125,050	127,571
Amortizable Intangible Liabilities
Amortizable Intangible Liabilities, Gross Carrying Amount	(150,211)	(147,232)
Amortizable Intangible Liabilities, Accumulated Amortization	46,560	43,391
Amortizable Intangible Liabilities, Net Carrying Amount	(103,651)	(103,841)
Above-market Ground Lease, Gross	(671)	(671)
Above-market Ground Lease, Accumulated Amortization	49	34
Above-market Ground Lease, Net	(622)	(637)
Finite-Lived Intangible Liabilities, Gross	(150,882)	(147,903)
Finite-Lived Intangible Liabilities, Accumulated Amortization	46,609	43,425
Finite-Lived Intangible Liabilities, Net	(104,273)	(104,478)
Below market rents, acquired	$ 3,000	$ 10,900
Below market rents acquired, weighted average useful life	25 years 8 months	12 years 1 month
Above-market ground lease, acquired		$ 700
Above-market ground lease acquired, weighted average useful life		11 years 6 months
In-place lease intangible assets
Finite-Lived Intangible Assets [Line Items]
Amortizable Intangible Assets, Gross Carrying Amount	$ 199,740	$ 193,821
Amortizable Intangible Assets, Accumulated Amortization	(81,262)	(72,749)
Amortizable Intangible Assets, Net Carrying Amount	118,478	121,072
Intangible assets acquired	$ 5,900	$ 41,600
Acquired intangible assets, weighted average useful life	4 years 7 months	4 years 1 month
Above-market rent
Finite-Lived Intangible Assets [Line Items]
Amortizable Intangible Assets, Gross Carrying Amount	$ 17,366	$ 16,786
Amortizable Intangible Assets, Accumulated Amortization	(10,794)	(10,287)
Amortizable Intangible Assets, Net Carrying Amount	6,572	6,499
Intangible assets acquired	$ 600	$ 2,700
Acquired intangible assets, weighted average useful life	1 year 1 month	4 years 9 months