Impairment Charges, Impairment of Joint Venture Investments and Reserves - Impairment Charges on Assets or Investments (Parenthetical) (Detail) - Operating Shopping Centers [Member] - ShoppingCenter	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Investments [Line Items]
Number of properties impaired		20	25
United States and Puerto Rico [Member]
Schedule Of Investments [Line Items]
Number of properties impaired	27