Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 sqft Property
Development Activity [Abstract]
Approximate Square Feet	13,600,000
Development Activity [Member]
Development Activity [Abstract]
Number of Properties	14
Approximate Square Feet	1,668,716
Funded During Year Ended December 31, 2012	$ 116,444
Total Amount Funded Through December 31, 2012	524,382
Estimated Remaining Budget
Construction mortgage loans [Member]
Development Activity [Abstract]
Number of Properties	2
Approximate Square Feet	386,000
Funded During Year Ended December 31, 2012	77,985
Total Amount Funded Through December 31, 2012	118,441
Estimated Remaining Budget	84,173
Stabilization in progress [Member]
Development Activity [Abstract]
Number of Properties	12
Approximate Square Feet	1,282,716
Funded During Year Ended December 31, 2012	38,459
Total Amount Funded Through December 31, 2012	405,941
Stabilization in progress [Member] | Minimum [Member]
Development Activity [Abstract]
Estimated Remaining Budget	35,000
Stabilization in progress [Member] | Maximum [Member]
Development Activity [Abstract]
Estimated Remaining Budget	45,000
Construction in progress [Member]
Development Activity [Abstract]
Number of Properties	0
Approximate Square Feet	0
Funded During Year Ended December 31, 2012	0
Total Amount Funded Through December 31, 2012	0
Estimated Remaining Budget	$ 0