Quarterly Financial Data (Unaudited): (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended			3 Months Ended	0 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 SDG Properties	Oct. 03, 2012 FlatIron Crossing	Dec. 31, 2012 FlatIron Crossing	Oct. 26, 2012 Arrowhead Towne Center	Dec. 31, 2012 Arrowhead Towne Center
Quarterly Financial Data (Unaudited):
Revenues	$ 251,165	$ 215,669	$ 204,545	$ 214,729	$ 208,479	$ 193,319	$ 181,299	$ 185,265	$ 881,323	$ 763,371	$ 711,557
Net income (loss) attributable to common stockholders	174,247	43,893	133,354	(14,068)	163,107	12,941	(19,216)	34	337,426	156,866	25,190
Net income (loss) attributable to common stockholders per share-basic (in dollars per share)	$ 1.27	$ 0.33	$ 1.00	$ (0.11)	$ 1.23	$ 0.10	$ (0.15)		$ 2.51	$ 1.18	$ 0.19
Net income (loss) attributable to common stockholders per share-diluted (in dollars per share)	$ 1.27	$ 0.33	$ 1.00	$ (0.11)	$ 1.23	$ 0.10	$ (0.15)		$ 2.51	$ 1.18	$ 0.19
Quarterly Financial Data (Unaudited)
Remeasurement gain on acquisition of additional interest									115,729				84,227	84,227	115,729	115,729
Remeasurement gain on acquisition of additional interest									29,301	389,707	576	188,264
Impairment loss related to the reduction of the expected holding period of certain long-lived assets										$ 25,216