Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
OPERATING ACTIVITIES
Net income (loss)	$ (184)	$ 8,247	$ 51,148
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Depreciation and amortization	92,388	77,894	70,921
Stock-based compensation	2,922	2,411	3,711
Straight-line rent receivable	(4,630)	(2,472)	(1,925)
Straight-line rent liability	488	92	444
Gain on sales of real estate properties	(7,035)	(8,352)	(20,136)
Loss on extinguishment of debt	1,986	480
Re-measurement gain of equity interest upon acquisition			(2,701)
Impairments	6,697	1,259	22
Provision for bad debt, net	(160)	(409)	517
Payment of partial pension settlement		(2,582)	(2,300)
Changes in operating assets and liabilities
Other assets	(7,993)	(9,137)	(1,015)
Accounts payable and accrued liabilities	10,770	5,834	4,453
Other liabilities	9,783	1,318	75
Net cash provided by operating activities	105,032	80,835	103,214
INVESTING ACTIVITIES
Acquisition and development of real estate properties	(230,106)	(369,034)	(170,520)
Funding of mortgages and notes receivable	(101,931)	(25,109)	(23,391)
Investments in unconsolidated joint venture			(184)
Proceeds from sales of real estate	19,572	34,512	83,441
Proceeds from mortgages and notes receivable repayments	17,797	9,201	12,893
Net cash used in investing activities	(294,668)	(350,430)	(97,761)
FINANCING ACTIVITIES
Net borrowings (repayments) on unsecured credit facility	212,000	(50,000)	(279,000)
Borrowings on notes and bonds payable		396,800	377,969
Repayments on notes and bonds payable	(3,703)	(2,516)	(28,433)
Repurchase of notes payable	(280,201)	(8,556)
Dividends paid	(89,270)	(75,821)	(91,385)
Proceeds from issuance of common stock	251,916	118,205	26,464
Common stock redemptions	(86)		(8)
Capital contributions received from noncontrolling interests		633	2,228
Distributions to noncontrolling interest holders	(284)	(481)	(282)
Purchase of noncontrolling interests	(1,591)
Debt issuance and assumption costs	(7,728)	(1,199)	(11,293)
Net cash provided by (used in) financing activities	81,053	377,065	(3,740)
Increase (decrease) in cash and cash equivalents	(108,583)	107,470	1,713
Cash and cash equivalents, beginning of period	113,321	5,851	4,138
Cash and cash equivalents, end of period	4,738	113,321	5,851
Supplemental Cash Flow Information:
Interest paid	73,157	62,274	50,052
Capitalized interest	8,531	10,315	10,087
Company-financed real estate property sales	2,700
Invoices accrued for construction, tenant improvement and other capitalized costs	12,131	13,555	16,266
Mortgage notes payable assumed upon acquisition (adjusted to fair value)	54,392	24,268	11,716
Mortgage note payable disposed of upon sale of joint venture interest			5,425
Foreclosure of mortgage notes receivable	4,371
Elimination of mortgage note upon consolidation of variable interest entities	$ 21,939