Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012 Property		Jun. 30, 2012 sqft Property
Development Activity [Abstract]
Number of Properties	1		1
Estimated Total Investment	$ 13,959		$ 13,959
Approximate Square Feet			13,500,000
Construction in Progress [Member]
Development Activity [Abstract]
Number of Properties	1	[1]	1	[1]
Funded	2,169	[1]
Total Amount Funded	9,009	[1]	9,009	[1]
Estimated Remaining Fundings			4,950	[1]
Estimated Total Investment	13,959	[1]	13,959	[1]
Approximate Square Feet			96,433	[1]
Mortgage construction notes [Member]
Development Activity [Abstract]
Number of Properties	2		2
Funded	15,597
Total Amount Funded	68,694		68,694
Estimated Remaining Fundings			133,920
Estimated Total Investment	202,614		202,614
Approximate Square Feet			386,000
Stabilization in Progress [Member]
Development Activity [Abstract]
Number of Properties	11	[1]	11	[1]
Funded	6,979	[1]
Total Amount Funded	379,494	[1]	379,494	[1]
Estimated Remaining Fundings			16,532	[1]
Estimated Total Investment	396,026	[1]	396,026	[1]
Approximate Square Feet			1,185,863	[1]
Land Held for Development [Member]
Development Activity [Abstract]
Funded	0
Total Amount Funded	25,171		25,171
Development Activity [Member]
Development Activity [Abstract]
Number of Properties	14		14
Funded	24,745
Total Amount Funded	482,368		482,368
Estimated Remaining Fundings			155,402
Estimated Total Investment	$ 612,599		$ 612,599
Approximate Square Feet			1,668,296

[1] The estimated total budget for the development properties reflects the original budget including estimated tenant improvement allowances but does not include any estimate of excess tenant improvement cost financing by the Company. To the extent actual amounts funded for the development properties reflect excess tenant improvement costs financed by the Company, the estimated remaining fundings could be greater than the amount budgeted.