Reportable Segments (Reconciliation of Net Income to Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net Operating Income	$ 87,731	$ 80,578
Net operating income from unconsolidated joint ventures	(7,873)	(7,421)
Revenues	132,733	117,202
Reimbursed expenses	(932)	(942)
General and administrative expenses	(11,460)	(6,809)
Interest expense	(10,820)	(9,778)
Depreciation and amortization	(45,861)	(45,093)
Acquisition and transaction costs	(3)	(91)
Loss on extinguishment of debt	0	(85)
Other expenses	(180)	(320)
Income from unconsolidated joint ventures	2,904	2,885
Gain (loss) on sale of investment properties	13,111	(372)
Net income	36,005	16,406
Fee income
Segment Reporting Information [Line Items]
Revenues	8,728	2,894
Other
Segment Reporting Information [Line Items]
Revenues	$ 660	$ 960