Fair Value Measurements Fair Value Level 3 Rollforward (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended					6 Months Ended		12 Months Ended		6 Months Ended	12 Months Ended				6 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012	Jun. 30, 2013 Government and government sponsored entities [Member]		Dec. 31, 2012 Government and government sponsored entities [Member]		Jun. 30, 2013 Cost-method Investments [Member]	Dec. 31, 2012 Cost-method Investments [Member]	Dec. 31, 2011 Cost-method Investments [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Government and government sponsored entities [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Government and government sponsored entities [Member]	Dec. 31, 2011 Fair Value, Inputs, Level 3 [Member] Government and government sponsored entities [Member]	Jun. 30, 2013 Citadel Mall [Member]	Dec. 31, 2012 Citadel Mall [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assumed Capitalization Rate Range Used To Determine Fair Value					10% to 12%
Asset Impairment Charges					$ 585
Depreciation					(894)
Fair Value of Investments In Real Estate																						23,900	45,178
Payments for Capital Improvements	134,798	[1]	118,556	[1]	196,607	[1]	154,044	[1]														69
Cost Method Investments, Fair Value Disclosure									2,475					0	2,475	2,475		2,475
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements										0		1,542
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3										(121)	[2]	(2,248)	[2]
Fair value of available-for-sale securities	16,304				16,304				27,679			11,123					0	11,123	0	11,123	11,829
Proceeds from sales of available-for-sale securities					15,877		0							(4,875)					(11,002)
Gain on investments	2,400		0		2,400		0							2,400
Impairment of Real Estate	$ (21,038)		$ 0		$ (21,038)		$ 0								$ (2,400)							$ (20,453)

[1] (3) Amounts include acquisitions of real estate assets and investments in unconsolidated affiliates. Developments in progress are included in the All Other category.

[2] (1)The TIF bonds were adjusted to their net realizable value as of December 31, 2012 and were redeemed in January 2013. The difference in estimate was recorded as a transfer to real estate assets.