Schedule III- Real Estate and Accumulated Depreciation Schedule III - Real Estate and Accumulated Depreciation - Rollforward of Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward]
Balance as of the beginning of the year	$ 734,783	$ 581,505	$ 474,223
Additions	202,837	171,545	117,282
Dispositions	(55,132)	(18,267)	(10,000)
Balance as of the end of the year	882,488	734,783	581,505
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Accumulated depreciation lease intangibles	$ 325,700	$ 286,900	$ 236,100
Tenant Improvements | Minimum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Estimated useful life	1 month
Tenant Improvements | Maximum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Estimated useful life	166 months
Furniture, fixtures and equipment
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Estimated useful life	5 years