Segment Information - Reconciliation of Consolidated Net Income to Consolidated NOI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting [Abstract]
Net income	$ 13,136	$ 7,698	$ 57,841	$ 28,969
Plus:
Interest expense	19,301	20,304	38,834	41,741
Interest expense - amortization of deferred financing costs	627	596	1,254	1,230
Depreciation and amortization	43,717	44,263	87,008	90,155
General and administrative expenses	7,523	6,659	16,246	15,984
Equity in (income) loss of Real Estate Ventures	358	(1,084)	1,183	(336)
Provision for impairment	0	327	0	3,057
Less:
Interest income	641	163	1,344	556
Income tax (provision) benefit	(20)	339	(158)	239
Net gain (loss) on disposition of real estate	(35)	1,088	(35)	8,411
Net gain on sale of undepreciated real estate	2,837	0	2,859	0
Net gain on Real Estate Venture transactions	0	0	37,263	14,582
Consolidated net operating income	$ 81,239	$ 77,173	$ 161,093	$ 157,012