Supplemental Cash Flow Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Disclosure of Cash Flow Information:
Interest paid	$ 38,560	$ 38,288	$ 30,438
Income taxes paid	1,090	1,045	345
Investing Activities:
Accrued capital expenditures	1,575	5,448	2,768
Note receivable included in the consideration for the acquisition of a building	37,264	0	0
The following represents the significant increase (decrease) in certain assets and liabilities in connection with our acquisitions of operating properties:
Debt, net	0	6,657	190,294
Net change in security deposits, prepaid rent and other liabilities	0	0	14,552
Issuance of operating partnership units in connection with Fannin acquisition	0	0	1,557
Financing Activities:
Issuance of common stock under the DRIP	31,916	75,864	56,551
Distributions declared, but not paid, including common stock issued under the DRIP	30,959	14,120	12,317
Adjustment to redeemable noncontrolling interests	$ 0	$ 0	$ (275)