Mortgages Payable (Details) (USD $)	9 Months Ended
	Sep. 30, 2011		Dec. 31, 2010
Mortgages Payable [Abstract]
Investment in new properties	$ 826,400,000
Deferred financing costs originally recorded for mortgages payable	917,000
Debt Instrument [Line Items]
Remaining Principal Balance	67,291,000	[1]
Amortized Premium (Discount) Balance	859,000
Mortgage Payable Balance	68,150,000
Floating variable interest rate, variable rate basis	1 month LIBOR
Floating variable interest rate, basis spread on variable rate (in hundredths)	4.50%
Mortgage interest rate payable, maximum (in hundredths)	5.50%
Note receivable assumed in connection with 2011 acquisition	8,780,000		0
Solae, LLC, Assumed Note Receivable Stated Interest Rate (in hundredths)	8.14%
Assumed mortgage payables	67,400,000
Net premiums recorded upon assumption of mortgages	957,000
Deferred financing costs remaining balance at period end	835,000
Aviall Services, Inc. Maturity 12-1-13 [Member]
Debt Instrument [Line Items]
Stated Interest Rate (in hundredths)	6.25%	[2],[3]
Effective Interest Rate (in hundredths)	4.96%	[2]
Maturity Date	Dec. 01, 2013	[1],[2]
Remaining Principal Balance	12,512,000	[1],[2]
Amortized Premium (Discount) Balance	406,000	[2]
Mortgage Payable Balance	12,918,000	[2]
Aviall Services, Inc. Maturity 9-1-14 [Member]
Debt Instrument [Line Items]
Stated Interest Rate (in hundredths)	6.25%	[2],[3]
Effective Interest Rate (in hundredths)	4.82%	[2]
Maturity Date	Sep. 01, 2014	[1],[2]
Remaining Principal Balance	11,710,000	[1],[2]
Amortized Premium (Discount) Balance	343,000	[2]
Mortgage Payable Balance	12,053,000	[2]
T- Mobile USA, Inc. [Member]
Debt Instrument [Line Items]
Stated Interest Rate (in hundredths)	5.89%	[3]
Effective Interest Rate (in hundredths)	5.15%
Maturity Date	May 06, 2014	[1]
Remaining Principal Balance	10,664,000	[1]
Amortized Premium (Discount) Balance	182,000
Mortgage Payable Balance	10,846,000
MeadWestvaco Corporation [Member]
Debt Instrument [Line Items]
Stated Interest Rate (in hundredths)	4.73%	[3]
Effective Interest Rate (in hundredths)	4.89%
Maturity Date	Jun. 10, 2015	[1]
Remaining Principal Balance	23,625,000	[1]
Amortized Premium (Discount) Balance	(72,000)
Mortgage Payable Balance	23,553,000
Solae, LLC Effective Rate 8.26% Note 1 [Member]
Debt Instrument [Line Items]
Stated Interest Rate (in hundredths)	8.26%	[2],[3],[4]
Effective Interest Rate (in hundredths)	8.26%	[2],[4]
Maturity Date	Dec. 28, 2013	[1],[2],[4]
Remaining Principal Balance	4,510,000	[1],[2],[4]
Amortized Premium (Discount) Balance	0	[2],[4]
Mortgage Payable Balance	4,510,000	[2],[4]
Solae, LLC Effective Rate 8.26% Note 2 [Member]
Debt Instrument [Line Items]
Stated Interest Rate (in hundredths)	8.26%	[2],[3],[4]
Effective Interest Rate (in hundredths)	8.26%	[2],[4]
Maturity Date	Dec. 28, 2013	[1],[2],[4]
Remaining Principal Balance	4,270,000	[1],[2],[4]
Amortized Premium (Discount) Balance	0	[2],[4]
Mortgage Payable Balance	$ 4,270,000	[2],[4]

[1] The mortgages require monthly payments, with a principal payment due at maturity.

[2] These are mortgages associated with one property occupied by the applicable tenant.

[3] With the exception of the MeadWestvaco Corporation mortgage, the mortgages are at fixed interest rates. The MeadWestvaco Corporation mortgage is at a floating variable interest rate calculated as the sum of the current 1 month LIBOR plus 4.50%, not to exceed an all-in interest rate of 5.5%.

[4] As part of the assumption of these mortgages payable related to our acquisition of Solae, LLC, we also assumed an $8.8 million note receivable, upon which we will receive interest income at a stated rate of 8.14% through December 28, 2013.