Notes Payable, Commitments and Contingencies (Details Textual) (USD $)	1 Months Ended	11 Months Ended	12 Months Ended								1 Months Ended			12 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended
	Feb. 28, 2010	Nov. 30, 2011 sqft	Dec. 31, 2011 Y	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Credit Facility, unsecured [Member]	Dec. 31, 2010 Credit Facility, unsecured [Member]	Dec. 31, 2011 Mahan Village [Member] sqft	Dec. 31, 2011 Maximum [Member] Credit Facility, unsecured [Member]	Dec. 31, 2011 Minimum [Member] Credit Facility, unsecured [Member]	Jul. 31, 2010 Meridian Mark Plaza [Member]	Sep. 30, 2011 Mahan Village [Member]	Dec. 31, 2011 Mahan Village [Member]	Dec. 31, 2010 Terminus 100 mortgage note [Member]	Dec. 31, 2011 Long term debt- nonrecourse [Member] Y	Dec. 31, 2007 Term Facility [Member]	Oct. 31, 2009 Interest Rate Swap [Member]	Dec. 31, 2010 Interest Rate Swap [Member]	Dec. 31, 2008 Interest Rate Swap [Member] Agreement	Dec. 31, 2009 Interest Rate Swap [Member]
Notes payable commitments and contingencies (Textual) [Abstract]
Mortgage loan principal amount											$ 22,300,000
Mortgage loan principal amount, revised											27,000,000
Interest rate on mortgage loan											8.27%		3.25%
Maximum amount available under construction loan agreement													15,000,000
Loss on extinguishment of debt and interest rate swaps			74,000	9,827,000	2,766,000
Interest rate on mortgage loan, revised											6.00%			5.25%
Amortization Period (Years)						5 years					30 years			30 years
Maturity date of debt instrument						Aug. 29, 2012					Aug. 01, 2020	Sep. 12, 2014		Jan. 01, 2023
Repayment of principal amount														40,000,000
Revised mortgage note balance														140,000,000
Interest rate on mortgage note														6.13%
Notes payable			539,442,000	509,509,000		198,250,000	105,400,000
Interest rate swap agreement, notional amount			568,500,000	521,800,000															75,000,000	75,000,000
Revised notional amount of interest rate derivatives																			40,000,000
Fixed base rate under interest rate swap agreement																5.01%	2.84%		2.84%
Number of interest rate swap agreement																			2
Payment to counterparty of swap agreement																	1,800,000		959,000
Expiry of swap agreement																2012-08	2009-10		2010-10
Pledged assets, carrying value															224,500,000
Non recourse debt															341,200,000
Weighted average maturity of consolidated debt															5.1
Spread over LIBOR			2.00%						2.25%	1.75%
Interest rate over LIBOR			the spread over LIBOR was 2.0%			LIBOR
Interest rate swap agreement, notional amount																100,000,000
Square footage of real estate property		775,000						147,000
Maximum percentage guaranteed under construction loan								25.00%
Administration fee to effect the amendment						438,000	1,700,000
Unamortized deferred loan costs related to previous facility							592,000
Payment to counterparty to the swap agreement																		9,200,000
Notes Payable Commitments and Contingencies (Additional Textual) [Abstract]
Previous borrowing capacity under the credit facility	600,000,000
Original maturity date of credit facility	8/29/2011
Previous minimum consolidated fixed charge coverage ratio	1.50
Reduced Minimum consolidated fixed charge coverage ratio	1.30
Outstanding commitments to fund real estate projects				26,800,000
Outstanding performance bonds			3,100,000
Future lease commitments			16,411,000
Lease operating expenses			680,000	865,000	765,000
Weighted average remaining terms of ground leases			71
Weighted average remaining terms of operating leases			1
Maximum borrowing capacity under credit facility	$ 350,000,000
Line of Credit Facility, Expiration Date	8/29/2012