Significant Accounting Policies - Rollforward Of Noncontrolling Interest, Simon Group Property, Inc. (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Noncontrolling interests:
Noncontrolling interests, beginning of period	$ 649,464	$ 744,905
Net income attributable to noncontrolling interests after preferred distributions and income attributable to redeemable noncontrolling interests in consolidated properties	72,945	81,459
Distributions to noncontrolling interest holders	(84,221)	(83,728)
Other comprehensive income (loss) allocable to noncontrolling interests:
Unrealized gain on derivative hedge agreements	(143)	(2,103)
Net loss reclassified from accumulated other comprehensive loss into earnings	345	20,146
Currency translation adjustments	1,618	2,696
Changes in available-for-sale securities and other	101	1,680
Other comprehensive income (loss)	1,921	22,419
Adjustment to limited partners' interest from change in ownership in the Operating Partnership	(33,235)	(5,143)
Units exchanged for common shares	(12)	(16)
Long-term incentive performance units	14,705	12,061
Contributions by noncontrolling interests, net, and other	171
Noncontrolling interests, end of period	$ 621,738	$ 771,957