Reportable Segments (Reconciliation of Net Income to Net Operating Income) (Details) - USD ($)	2 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting [Abstract]
Net Operating Income		$ 75,815,000	$ 61,621,000	$ 236,097,000	$ 180,142,000
Net operating income from unconsolidated joint ventures		(6,934,000)	(6,760,000)	(23,719,000)	(20,359,000)
Net operating income from discontinued operations		0	(26,408,000)	0	(76,852,000)
Fee income		2,597,000	1,945,000	6,387,000	5,968,000
Other income		993,000	153,000	9,593,000	570,000
Reimbursed expenses		(895,000)	(795,000)	(2,667,000)	(2,463,000)
General and administrative expenses		(7,193,000)	(4,368,000)	(21,993,000)	(17,301,000)
Interest expense		(7,587,000)	(5,754,000)	(25,851,000)	(16,562,000)
Depreciation and amortization		(47,622,000)	(16,622,000)	(152,546,000)	(49,804,000)
Acquisition and transaction costs		677,000	(1,446,000)	(1,499,000)	(3,889,000)
Gain on extinguishment of debt	$ 2,300,000	429,000	0	2,258,000	0
Other expenses		(423,000)	(173,000)	(1,063,000)	(681,000)
Income from unconsolidated joint ventures		2,461,000	1,527,000	43,362,000	5,144,000
Gain (loss) on sale of investment properties		(33,000)	0	119,729,000	13,944,000
Income from discontinued operations		0	8,737,000	0	24,361,000
Net income		$ 12,285,000	$ 11,657,000	$ 188,088,000	$ 42,218,000