Investments in Unconsolidated Entities (Details) - USD ($) $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	[2]	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments In Unconsolidated Joint Ventures [Line Items]
Total revenues	$ 1,104,257	[1]	$ 1,091,483	$ 1,058,602	$ 1,062,298	$ 1,078,321	$ 1,079,133		$ 1,076,657	$ 1,047,050	$ 4,316,641	$ 4,281,160	$ 3,859,826
Net income											540,613	1,082,070	888,549
Net real estate investments	26,171,077					26,563,629					26,171,077	26,563,629
Total other assets	1,773,368					2,301,555					1,773,368	2,301,555
Total assets	27,944,445					28,865,184					27,944,445	28,865,184
Total liabilities	12,643,799					13,185,279					12,643,799	13,185,279
Redeemable noncontrolling interests	375,194					398,433					375,194	398,433
Total equity	14,925,452					15,281,472					14,925,452	15,281,472	15,175,885	$ 13,473,049
Non Controlling [Member]
Investments In Unconsolidated Joint Ventures [Line Items]
Total revenues											2,074,139	1,867,464	2,947,993
Net income											(264,473)	(86,167)	$ (40,116)
Net real estate investments	2,955,527					2,595,107					2,955,527	2,595,107
Total other assets	2,582,943					2,298,503					2,582,943	2,298,503
Total assets	5,538,470					4,893,610					5,538,470	4,893,610
Total liabilities	4,037,145					3,588,007					4,037,145	3,588,007
Total equity	$ 1,501,325					$ 1,305,603					$ 1,501,325	$ 1,305,603

[1] The decrease in net income (loss) and amounts per share are primarily attributable to $99,821,100 impairment of assets and $62,966,000 provision for loan losses recognized in the fourth quarter as compared to none in the third quarter.

[2] The increase in net income and amounts per share are primarily attributable to gains on sales of real estate of $162,351,000 for the third quarter as compared to gains of $1,530,000 for the second quarter.