Reportable Segments (Reconciliation of Net Income to Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net Operating Income	$ 97,417	$ 80,195	$ 185,148	$ 160,773
Net operating income from unconsolidated joint ventures	(9,379)	(7,228)	(17,252)	(14,649)
Revenues	142,020	116,628	274,753	233,830
Reimbursed expenses	(1,047)	(860)	(1,979)	(1,802)
General and administrative expenses	(8,374)	(8,071)	(19,834)	(14,880)
Interest expense	(12,059)	(9,714)	(22,879)	(19,492)
Depreciation and amortization	(50,904)	(45,675)	(96,765)	(90,768)
Acquisition and transaction costs	(49,827)	(137)	(49,830)	(228)
Other expenses	(624)	(44)	(804)	(364)
Income from unconsolidated joint ventures	3,634	5,036	6,538	7,921
Gain on sale of investment properties	1,304	5,317	14,415	4,945
Loss on extinguishment of debt	0	0	0	(85)
Net income (loss)	(22,582)	21,749	13,423	38,155
Fee income
Segment Reporting Information [Line Items]
Revenues	7,076	1,798	15,804	4,692
Termination fee income
Segment Reporting Information [Line Items]
Revenues	190	639	710	999
Other
Segment Reporting Information [Line Items]
Revenues	$ 11	$ 493	$ 151	$ 1,093