Mortgage and Other Indebtedness, Net - Narrative (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) associated_center mall subsidiary mortgage_note_receivable	Dec. 31, 2018 USD ($) unsecured_term_loan	Jan. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Debt Instrument [Line Items]
Number of malls securing the credit facility | mall	17
Number of associated centers securing the credit facility | associated_center	3
Number of wholly owned subsidiaries | subsidiary	36
Ownership interest in guarantor subsidiaries by Operating Partnership (as a percent)	100.00%
Principal maturities for remainder of fiscal year	$ 217,655,000
Weighted-average maturity period	4 years 5 months	3 years 8 months
Unsecured lines of credit
Debt Instrument [Line Items]
Number of debt instruments | unsecured_term_loan		3
Maximum borrowing capacity		$ 1,100,000,000
Variable-rate debt	$ 390,000,000
Unsecured term loans
Debt Instrument [Line Items]
Total Outstanding		$ 695,000,000	$ 500,000,000
Number of debt instruments | unsecured_term_loan		3
Non-recourse loans on operating properties
Debt Instrument [Line Items]
Total Outstanding	163,476,000
Default minimum of debt instrument	$ 50,000,000
Secured Debt | Line of Credit
Debt Instrument [Line Items]
Total Outstanding				$ 1,185,000,000
Interest rate (as a percent)	4.74%
Quarterly installment payments on debt				35,000,000
Secured Debt | Line of Credit | Minimum
Debt Instrument [Line Items]
Annual facility fee (as a percent)	0.25%
Secured Debt | Line of Credit | Maximum
Debt Instrument [Line Items]
Annual facility fee (as a percent)	0.35%
Secured Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Total Outstanding				685,000,000
Secured Debt | Unsecured term loans
Debt Instrument [Line Items]
Total Outstanding				500,000,000
LIBOR | Unsecured Term Loan 1
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.25%
Guarantor Subsidiaries
Debt Instrument [Line Items]
Number of malls securing the credit facility | mall	17
Number of associated centers securing the credit facility | associated_center	3
Number of wholly owned subsidiaries | subsidiary	36
Number of malls not classified as collateral for the secured credit facility | mall	5
Number of associated centers not classified as collateral for the secured credit facility | associated_center	2
Number of mortgage notes receivable not classified as collateral for the secured credit facility | mortgage_note_receivable	4
Principal maturities for remainder of fiscal year	$ 71,187,000
Weighted-average maturity period	2 years 1 month 10 days	1 year 29 days
Guarantor Subsidiaries | Secured Debt | Line of Credit
Debt Instrument [Line Items]
Total Outstanding				$ 1,185,000