Supplemental Disclosure of Non-Cash Investing and Financing Activities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Issuance of common stock as deferred compensation		$ 473
Issuance of units in the operating partnership	777	1,131
Redemption of units in the operating partnership	17,287	275
Derivative instruments at fair value	128	288
Mortgage assigned upon asset sale		59,099
Tenant improvements and capital expenditures payable	9,136	11,941
Fair value adjustment to noncontrolling interest in operating partnership	24,016	41,935
Deferred leasing payable	741	2,457
Capital leased asset	$ 6,859