Combined Guarantor Subsidiaries - Combined Balance Sheets - Summary (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018		Mar. 31, 2018	Dec. 31, 2017
Real estate assets:
Land	[1]	$ 783,055	$ 793,944
Buildings and improvements	[1]	6,248,286	6,414,886
Real estate assets	[1]	7,031,341	7,208,830
Accumulated depreciation	[1]	(2,478,821)	(2,493,082)
Real estate investment property, net, before developments in progress	[1]	4,552,520	4,715,748
Developments in progress	[1]	56,273	38,807
Net investment in real estate assets	[1]	4,622,964	4,785,526
Cash and cash equivalents		21,055	25,138	[1]	$ 23,346
Receivables:
Tenant, net of allowance for doubtful accounts of $2,337 in 2018	[1]	71,358	77,788
Other, net of allowance for doubtful accounts of $838 in 2018	[1]	9,855	7,511
Mortgage and other notes receivable	[1]	7,406	7,672
Intangible lease assets and other assets	[1]	151,953	153,665
Total assets	[1]	5,161,948	5,340,853
LIABILITIES, REDEEMABLE NONCONTROLLING INTERESTS AND EQUITY
Mortgage notes payable, net		3,898,550	4,043,180
Accounts payable and accrued liabilities		277,256	218,217
Total liabilities	[1]	4,200,459	4,305,113
Commitments and contingencies (Note 7 and Note 11)
Total liabilities, redeemable noncontrolling interests and equity		5,161,948	5,340,853
Guarantor Subsidiaries
Real estate assets:
Land		221,773	232,813
Buildings and improvements		2,218,595	2,361,707
Real estate assets		2,440,368	2,594,520
Accumulated depreciation		(880,724)	(921,562)
Real estate investment property, net, before developments in progress		1,559,644	1,672,958
Developments in progress		8,083	6,582
Net investment in real estate assets		1,567,727	1,679,540
Cash and cash equivalents		8,057	5,880		5,085
Receivables:
Tenant, net of allowance for doubtful accounts of $2,337 in 2018		28,302	30,553
Other, net of allowance for doubtful accounts of $838 in 2018		1,063	1,007
Mortgage and other notes receivable		76,729	76,747
Intangible lease assets and other assets		42,218	48,133
Total assets		1,724,096	1,841,860
LIABILITIES, REDEEMABLE NONCONTROLLING INTERESTS AND EQUITY
Mortgage notes payable, net		256,078	377,996
Accounts payable and accrued liabilities		34,416	59,241
Total liabilities		290,494	437,237
Commitments and contingencies (Note 7 and Note 11)
Owners' equity		1,433,602	1,404,623		$ 1,509,846	$ 1,486,164
Total liabilities, redeemable noncontrolling interests and equity		$ 1,724,096	$ 1,841,860

[1] As of March 31, 2019, includes $609,856 of assets related to consolidated variable interest entities that can be used only to settle obligations of the consolidated variable interest entities and $406,466 of liabilities of consolidated variable interest entities for which creditors do not have recourse to the general credit of the Company. See Note 7.