Per Share and Per Unit Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Per Share And Per Unit Data
Net Income attributable to Common Stockholders - Basic		$ 712,796	$ 556,267	$ 547,004	$ 620,654	$ 571,116	$ 513,783	$ 381,990	$ 477,736	$ 2,436,721	$ 1,944,625	$ 1,835,559
Net Income attributable to Common Stockholders - Diluted										$ 2,436,721	$ 1,944,625	$ 1,835,559
Weighted Average Shares Outstanding — Basic and Diluted		309,293,708	309,294,045	309,355,154	310,583,643	310,855,573	310,853,299	311,579,301	312,809,981	309,627,178	311,517,345	312,690,756
Dividends
Total dividends paid per common share (in dollars per share)										$ 7.90	$ 7.15	$ 6.50
Percent taxable as ordinary income										96.20%	100.00%	99.70%
Percent taxable as long-term capital gains										3.80%	0.00%	0.30%
Total percentage of dividends paid										100.00%	100.00%	100.00%
Dividends declared per common share (in dollars per share)	$ 2.05
Simon Property Group, L.P.
Per Share And Per Unit Data
Net Income attributable to Common Stockholders - Basic		$ 821,237	$ 640,402	$ 629,822	$ 714,303	$ 657,774	$ 591,872	$ 439,986	$ 550,006	$ 2,805,764	$ 2,239,638	$ 2,122,236
Net Income attributable to Common Stockholders - Diluted										$ 2,805,764	$ 2,239,638	$ 2,122,236
Weighted Average Shares Outstanding — Basic and Diluted		356,396,387	356,073,080	356,181,817	357,446,988	358,025,108	358,115,572	358,865,806	360,130,442	356,520,452	358,776,632	361,526,633