Summary of Significant Accounting Policies - Rollforward Of Noncontrolling Interest, Simon Group Property, Inc. (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Noncontrolling interests:
Noncontrolling interests, beginning of period	$ 527,430	$ 621,738	$ 552,596	$ 649,464
Net income attributable to noncontrolling interests after preferred distributions and income attributable to redeemable noncontrolling interests in consolidated properties	83,037	58,393	177,213	131,338
Distributions to noncontrolling interest holders	(91,901)	(83,680)	(183,913)	(167,901)
Other comprehensive (loss) income allocable to noncontrolling interests:
Unrealized gain (loss) on derivative hedge agreements	2,797	(2,837)	1,993	(2,981)
Net loss reclassified from accumulated other comprehensive loss into earnings	288	322	571	668
Currency translation adjustments	(5,034)	2,181	(3,371)	3,799
Changes in available-for-sale securities and other	29	(150)	(9)	(49)
Other comprehensive income (loss)	(1,920)	(484)	(816)	1,437
Adjustment to limited partners' interest from change in ownership in the Operating Partnership	(16,496)	(35,100)	(52,717)	(68,335)
Units exchanged for common shares		(1,341)	(70)	(1,353)
Units redeemed	(98)		(572)
Long-term incentive performance units	7,462	4,853	15,769	19,558
Contributions by noncontrolling nonredeemable interests, net, and other	90	65	114	236
Noncontrolling interests, end of period	$ 507,604	$ 564,444	$ 507,604	$ 564,444