Investments in Real Estate Partnerships - Schedule of Acquisitions by Real Estate Partnerships (Details) (USD $)	12 Months Ended			9 Months Ended	12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013 BRE Throne Holdings LLC (BRET) [Member]	Dec. 31, 2013 BRE Throne Holdings LLC (BRET) [Member]	Dec. 31, 2012 BRE Throne Holdings LLC (BRET) [Member]	Jul. 25, 2012 BRE Throne Holdings LLC (BRET) [Member]	Dec. 31, 2013 GRI - Regency, LLC [Member]	Dec. 31, 2012 GRI - Regency, LLC [Member]	Dec. 31, 2013 Other Investments in Real Estate Partnerships [Member]	Dec. 31, 2012 Other Investments in Real Estate Partnerships [Member]	Dec. 31, 2013 RegCal, LLC [Member]	Dec. 31, 2012 RegCal, LLC [Member]	Dec. 31, 2013 Columbia Regency Partners II, LLC [Member]	Dec. 31, 2012 Columbia Regency Partners II, LLC [Member]	Dec. 31, 2013 Unconsolidated Properties [Member]	Dec. 31, 2012 Unconsolidated Properties [Member]	Dec. 31, 2011 Unconsolidated Properties [Member]	Dec. 31, 2013 Corporate Joint Venture [Member]	Dec. 31, 2012 Corporate Joint Venture [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] Lake Grove Commons [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] Applewood Village Shops [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] Village Plaza [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] Phillips Place [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] Tysons CVS [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] GRI - Regency, LLC [Member] Lake Grove Commons [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] GRI - Regency, LLC [Member] Applewood Village Shops [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] Jay Donegan [Member] Tysons CVS [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] Columbia Regency Partners II, LLC [Member] Village Plaza [Member]	Dec. 31, 2012 Corporate Joint Venture [Member] Johnny Harris [Member] Phillips Place [Member]	Dec. 31, 2013 Partnership Interest [Member]	Dec. 31, 2012 Partnership Interest [Member]	Dec. 31, 2011 Partnership Interest [Member]	Dec. 31, 2013 Gain on sale of real estate investments [Member]	Dec. 31, 2012 Gain on sale of real estate investments [Member]	Dec. 31, 2011 Gain on sale of real estate investments [Member]	Dec. 31, 2013 Operating Segments [Member] property	Dec. 31, 2012 Operating Segments [Member] property	Dec. 31, 2011 Operating Segments [Member] property	Dec. 31, 2013 Operating Segments [Member] Unconsolidated Properties [Member] property	Dec. 31, 2012 Operating Segments [Member] Unconsolidated Properties [Member] property	Dec. 31, 2011 Operating Segments [Member] Unconsolidated Properties [Member] property	Dec. 31, 2013 Land [Member] property	Dec. 31, 2012 Land [Member] property	Dec. 31, 2011 Land [Member] property	Dec. 31, 2013 Land [Member] Unconsolidated Properties [Member] property	Dec. 31, 2012 Land [Member] Unconsolidated Properties [Member] property	Dec. 31, 2011 Land [Member] Unconsolidated Properties [Member] property
Business Acquisition [Line Items]
Proceeds from sale of real estate investments	$ 212,632,000	$ 352,707,000	$ 86,233,000													$ 145,295,000	$ 119,275,000	$ 43,710,000
Gain on sale of real estate	15,695,000	40,437,000	7,464,000
Equity in income of investments in real estate partnerships (note 4)	31,718,000	23,807,000	9,643,000		4,499,000	2,211,000		12,789,000	9,311,000	2,146,000	1,807,000	332,000	540,000	1,274,000	290,000																31,718,000	23,807,000	9,643,000	3,847,000	8,962,000	2,114,000
Business Acquisition, Effective Date of Acquisition																					Jan. 17, 2012	Nov. 28, 2012	Dec. 19, 2012	Dec. 28, 2012	Jun. 20, 2012
Business Acquisition, Name of Acquired Entity																					Lake Grove Commons	Applewood Village Shops	Village Plaza	Phillips Place	Tysons CVS
Business Acquisition Location, City and State																					Lake Grove, NY	Wheat Ridge, CO	Chapel Hill, NC	Charlotte, NC	Vienna, VA
Business Acquisition, Property type																					Operating	Operating	Operating	Operating	Operating
Business Acquisition, Description of Acquired Entity																										GRIR	GRIR	Other	Columbia II	Other
Equity Method Investment, Ownership Percentage					0.00%	0.00%		0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%						0.00%	0.00%	0.00%	0.00%	0.00%
Mortgage loans assumed for the acquisition of real estate																			7,496,000	76,313,000	31,813,000	0	0	44,500,000	0
Acquired Finite-lived Intangible Asset, Amount																			8,438,000	8,002,000	5,397,000	363,000	2,242,000	0	0
Acquired Finite Lived Intangible Liability Amount																			332,000	5,062,000	4,342,000	34,000	686,000	0	0
Proceeds from Sale of Real Estate						321,000,000
Investments in real estate partnerships (note 4)	358,849,000	442,927,000			0	48,757,000	47,500,000	250,118,000	272,044,000	47,761,000	46,506,000	15,576,000	15,602,000	8,797,000	8,660,000																358,849,000	442,927,000
Preferred Stock, Dividend Rate, Percentage				10.50%
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds																			$ 13,600,000	$ 164,600,000	$ 72,500,000	$ 3,700,000	$ 19,200,000	$ 55,400,000	$ 13,800,000
Number of Real Estate Properties Sold																																					12	20	8	15	7	5	10	7	8	3	1	1
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest																100.00%	100.00%	100.00%