Combined Guarantor Subsidiaries - Combined Balance Sheets - Summary (Details) - USD ($) $ in Thousands		Sep. 30, 2019		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Real estate assets:
Land	[1]	$ 741,060				$ 793,944
Buildings and improvements	[1]	5,819,655				6,414,886
Real estate assets	[1]	6,560,715				7,208,830
Accumulated depreciation	[1]	(2,404,565)				(2,493,082)
Real estate investment property, net, before developments in progress	[1]	4,156,150				4,715,748
Developments in progress	[1]	63,891				38,807
Net investment in real estate assets	[1]	4,220,041				4,785,526
Cash and cash equivalents		34,565	[1]			25,138	[1]	$ 20,695
Receivables:
Tenant, net of allowance for doubtful accounts of $2,337 in 2018	[1]	76,947				77,788
Other, net of allowance for doubtful accounts of $838 in 2018	[1]	6,577				7,511
Mortgages	[1]	5,818				7,672
Intangible lease assets and other assets	[1]	146,036				153,665
Total assets	[1]	4,769,918				5,340,853
LIABILITIES, REDEEMABLE NONCONTROLLING INTERESTS AND EQUITY
Mortgage notes payable, net		3,699,007				4,043,180
Accounts payable and accrued liabilities		260,264				218,217
Total liabilities	[1]	3,959,271				4,305,113
Commitments and contingencies (Note 7 and Note 11)
Total liabilities, redeemable noncontrolling interests and equity		4,769,918				5,340,853
Guarantor Subsidiaries
Real estate assets:
Land		220,971				232,813
Buildings and improvements		2,257,597				2,361,707
Real estate assets		2,478,568				2,594,520
Accumulated depreciation		(942,870)				(921,562)
Real estate investment property, net, before developments in progress		1,535,698				1,672,958
Developments in progress		11,758				6,582
Net investment in real estate assets		1,547,456				1,679,540
Cash and cash equivalents		9,796				5,880		2,954
Receivables:
Tenant, net of allowance for doubtful accounts of $2,337 in 2018		28,896				30,553
Other, net of allowance for doubtful accounts of $838 in 2018		1,134				1,007
Mortgages		64,002				76,747
Intangible lease assets and other assets		41,419				48,133
Total assets		1,692,703				1,841,860
LIABILITIES, REDEEMABLE NONCONTROLLING INTERESTS AND EQUITY
Mortgage notes payable, net		251,773				377,996
Accounts payable and accrued liabilities		47,063				59,241
Total liabilities		298,836				437,237
Commitments and contingencies (Note 7 and Note 11)
Owners' equity		1,393,867		$ 1,416,003	$ 1,433,602	1,404,623		$ 1,425,649	$ 1,499,229	$ 1,509,846	$ 1,486,164
Total liabilities, redeemable noncontrolling interests and equity		$ 1,692,703				$ 1,841,860

[1] As of September 30, 2019, includes $484,345 of assets related to consolidated variable interest entities that can be used only to settle obligations of the consolidated variable interest entities and $346,999 of liabilities of consolidated variable interest entities for which creditors do not have recourse to the general credit of the Company. See Note 7.