Reportable Segments (Reconciliation of Net Income to Net Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting [Abstract]
Net Operating Income	$ 80,578	$ 80,167
Net operating income from unconsolidated joint ventures	(7,421)	(9,176)
Fee income	2,894	1,936
Other income	960	5,426
Reimbursed expenses	(942)	(865)
General and administrative expenses	(6,809)	(6,182)
Interest expense	(9,778)	(9,741)
Depreciation and amortization	(45,093)	(54,884)
Acquisition and transaction costs	(91)	(1,930)
Loss on extinguishment of debt	(85)	0
Other expenses	(320)	(404)
Income from unconsolidated joint ventures	2,885	581
Loss on sale of investment properties	(372)	(70)
Net income	$ 16,406	$ 4,858