Mortgage Notes Payable: (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		0 Months Ended	12 Months Ended	0 Months Ended		12 Months Ended		0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended				12 Months Ended		12 Months Ended		0 Months Ended	12 Months Ended			12 Months Ended		12 Months Ended		0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended		0 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Oct. 26, 2012 Arrowhead Towne Center	Dec. 31, 2012 Arrowhead Towne Center	Oct. 26, 2012 Arrowhead Towne Center	Jun. 29, 2012 Chandler Fashion Center	Dec. 31, 2012 Chandler Fashion Center	Dec. 31, 2011 Chandler Fashion Center	Sep. 17, 2012 Chesterfield Towne Center	Dec. 31, 2012 Chesterfield Towne Center	Dec. 31, 2012 Danbury Fair Mall	Dec. 31, 2011 Danbury Fair Mall	Dec. 05, 2012 Deptford Mall One	Dec. 31, 2012 Deptford Mall One	Dec. 31, 2011 Deptford Mall One	Dec. 31, 2012 Deptford Mall Two	Dec. 31, 2011 Deptford Mall Two	Dec. 31, 2012 Eastland Mall	Dec. 31, 2011 Eastland Mall	Dec. 31, 2012 Fashion Outlets of Chicago	Dec. 31, 2012 Fashion Outlets of Niagara Falls USA	Dec. 31, 2011 Fashion Outlets of Niagara Falls USA	Dec. 31, 2012 Fiesta Mall	Dec. 31, 2011 Fiesta Mall	Dec. 31, 2012 Flagstaff Mall	Dec. 31, 2011 Flagstaff Mall	Dec. 31, 2012 FlatIron Crossing	Oct. 03, 2012 FlatIron Crossing	Dec. 31, 2012 Freehold Raceway Mall	Dec. 31, 2011 Freehold Raceway Mall	Dec. 31, 2012 Fresno Fashion Fair	Dec. 31, 2011 Fresno Fashion Fair	Dec. 31, 2012 Great Northern Mall	Dec. 31, 2011 Great Northern Mall	Nov. 28, 2012 Kings Plaza	Dec. 31, 2012 Kings Plaza	Jan. 03, 2013 Kings Plaza Subsequent event	Mar. 23, 2012 Northgate Mall	Dec. 31, 2012 Northgate Mall	Dec. 31, 2011 Northgate Mall	May 17, 2012 The Oaks	Dec. 31, 2012 The Oaks	Dec. 31, 2011 The Oaks	Mar. 30, 2012 Pacific View	Dec. 31, 2012 Pacific View	Dec. 31, 2012 Paradise Valley Mall	Dec. 31, 2011 Paradise Valley Mall	Dec. 31, 2011 Prescott Gateway	Dec. 31, 2012 Promenade at Casa Grande	Dec. 31, 2011 Promenade at Casa Grande	Dec. 31, 2012 Salisbury Center	Dec. 31, 2011 Salisbury Center	Dec. 28, 2012 Santa Monica Place	Dec. 31, 2012 Santa Monica Place	Dec. 31, 2012 SanTan Village Regional Center.	Dec. 31, 2011 SanTan Village Regional Center.	Dec. 31, 2012 South Plains Mall	Dec. 31, 2011 South Plains Mall	Dec. 31, 2012 South Towne center	Dec. 31, 2011 South Towne center	Oct. 26, 2012 Towne Mall	Dec. 31, 2012 Towne Mall	Dec. 31, 2011 Towne Mall	Feb. 01, 2012 Tucson La Encantada	Dec. 31, 2012 Tucson La Encantada	Dec. 31, 2011 Tucson La Encantada	Dec. 31, 2012 Twenty Ninth Street	Dec. 31, 2011 Twenty Ninth Street	Dec. 31, 2012 Valley Mall	Dec. 31, 2011 Valley Mall	Dec. 31, 2012 Valley River Center	Dec. 31, 2011 Valley River Center	Dec. 31, 2011 Valley View Center	Dec. 31, 2012 Victor Valley, Mall	Dec. 31, 2011 Victor Valley, Mall	Dec. 31, 2012 Vintage Faire Mall	Dec. 31, 2011 Vintage Faire Mall	Sep. 06, 2012 Westside Pavilion	Dec. 31, 2012 Westside Pavilion	Dec. 31, 2011 Westside Pavilion	Dec. 31, 2012 Wilton Mall	Dec. 31, 2011 Wilton Mall
Mortgage loans payable on real estate
Carrying Amount of Mortgage Notes, Related Party	$ 274,609	$ 279,430										$ 119,823	$ 122,382																			$ 80,601	$ 81,733																																	$ 74,185	$ 75,315
Others	4,162,734	3,049,008			243,176			200,000	155,489		110,000	119,823	122,381		205,000	172,500	14,800	15,030	168,000	168,000	9,165	126,584	129,025	84,000	84,000	37,000	37,000	173,561		232,900	232,900	80,602	81,734	36,395	37,256		354,000			64,000	38,115		218,119	257,264		138,367	81,000	84,000	60,000	73,700	76,598	115,000	115,000		240,000	138,087	138,087	101,340	102,760	85,247	86,525		23,369	12,801				107,000	107,000	42,891	43,543	120,000	120,000	125,000	90,000	97,000	135,000	135,000		154,608	175,000	40,000	40,000
Effective Interest Rate (as a percent)					2.76%			3.77%			4.80%	5.53%			3.76%		6.46%		5.79%		3.00%	4.89%		4.98%		5.03%		1.96%		4.20%		6.76%		5.19%			3.67%			3.09%	7.00%		4.14%			4.08%	6.30%			5.21%		5.83%			2.99%	2.61%	2.69%	6.57%		6.39%			4.48%			4.23%		3.04%	3.12%	5.85%		5.59%			2.12%	2.13%	3.51%	3.56%		4.49%		1.22%	1.28%
Monthly Debt Service					1,131			625			573	1,538			948		101		811		22	727		341		151		1,102		805		1,104		234			2,229			132			1,064			668	625			280		555			1,004	266		648		554			117			368		252		280		558			137		352			783		32
Debt discounts															(19)	(25)																		(28)	(55)																																			(307)	(365)
Debt premiums					17,716																	7,270	8,198					5,232																																				88
Debt premiums (discounts), net	29,864	7,841
Ownership percentage purchased				33.30%
Fair value of loan assumed on acquisition						244,403																							175,720
Interest in the loan assumed by a third party (as a percent)								49.90%																						49.90%
Debt issued							200,000			110,000				205,000																						354,000		146,000	25,885			220,000			140,000									240,000								23,400			75,135														155,000
Interest rate on debt (as a percent)							3.77%
Mortgage notes payable, maximum borrowings																					140,000																500,000
Interest rate basis																					LIBOR																			LIBOR							LIBOR			LIBOR						LIBOR												LIBOR							LIBOR		LIBOR					LIBOR
Interest rate spread over basis (as a percent)																					2.50%																			2.25%							4.00%			4.00%						2.10%												2.63%							2.25%		3.00%					0.675%
Debt interest rate floor (as a percent)																																															5.50%
Interest rate basis floor (as a percent)																																																		0.50%
Interest expense capitalized	10,703	11,905	25,664
Fair value of mortgage notes payable	4,567,658	3,477,483
Deposit maintained with the lender																																																																																		$ 40,000
Period of loan maturities expected to be refinanced, restructured, extended or paid-off	12 months