Summary of Significant Accounting Policies - Rollforward Of Noncontrolling Interest, Simon Group Property L.P. (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Noncontrolling interests:
Net income attributable to noncontrolling nonredeemable interests	$ 84,452	$ 78,405	$ 261,665	$ 209,743
Distributions to noncontrolling nonredeemable interest holders	(93,637)	(86,125)	(277,550)	(254,026)
Contributions by noncontrolling nonredeemable interests, net, and other	47	51	161	287
Simon Property Group, L.P.
Noncontrolling interests:
Noncontrolling nonredeemable interests in properties, beginning of period	3,632	4,264	3,738	5,116
Net income attributable to noncontrolling nonredeemable interests	318	316	1,063	1,388
Distributions to noncontrolling nonredeemable interest holders	(56)	(800)	(1,020)	(2,960)
Contributions by noncontrolling nonredeemable interests, net, and other	48	51	161	287
Noncontrolling nonredeemable interests in properties, end of period	$ 3,942	$ 3,831	$ 3,942	$ 3,831