Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 sqft Property
Development Activity [Abstract]
Number of Properties	3
Estimated total investment	$ 83,282
Approximate Square Feet	13,700,000
Construction in Progress [Member]
Development Activity [Abstract]
Number of Properties	3
Amount funded	57,547
Funded amount for development activity	61,152
Estimated remaining fundings	22,130
Estimated total investment	83,282
Approximate Square Feet	300,614
Construction mortgage loans [Member]
Development Activity [Abstract]
Number of Properties	4
Amount funded	48,609
Funded amount for development activity	51,472
Estimated remaining fundings	165,722
Estimated total investment	217,194
Approximate Square Feet	473,431
Stabilization in Progress [Member]
Development Activity [Abstract]
Number of Properties	10
Amount funded	53,550
Funded amount for development activity	333,370
Estimated remaining fundings	26,288
Estimated total investment	359,658
Approximate Square Feet	1,095,284
Land Held for Development [Member]
Development Activity [Abstract]
Amount funded	4,403
Funded amount for development activity	25,176
Estimated total investment	0
Development Activity [Member]
Development Activity [Abstract]
Number of Properties	17
Amount funded	164,109
Funded amount for development activity	471,170
Estimated remaining fundings	214,140
Estimated total investment	$ 660,134
Approximate Square Feet	1,869,329