Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Cash Flows [Abstract]
Net income (loss)	$ 6,983	$ 5,535	$ (184)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	105,318	101,444	92,388
Stock-based compensation	5,210	3,492	2,922
Straight-line rent receivable	(8,608)	(6,013)	(4,630)
Straight-line rent liability	426	418	488
Gain on sales of real estate properties	(24,718)	(10,874)	(7,035)
Gain on sale of cost method investment in real estate	(1,492)	0	0
Loss on extinguishment of debt	29,907		1,986
Net gain from mortgage repayment by previously consolidated VIE	0	(313)	0
Impairments	9,889	14,908	6,697
Provision for bad debt, net	185	240	(160)
Changes in operating assets and liabilities:
Other assets	(5,660)	(3,469)	(5,173)
Accounts payable and accrued liabilities	740	(712)	10,770
Other liabilities	2,617	11,741	9,783
Net cash provided by operating activities	120,797	116,397	107,852
INVESTING ACTIVITIES
Acquisitions of real estate	(177,744)	(89,640)	(114,225)
Development of real estate	0	(7,833)	(83,720)
Tenant improvements and capital additions	(72,784)	(62,251)	(34,306)
Funding of mortgages and notes receivable	(58,731)	(78,297)	(101,931)
Proceeds from sales of real estate	96,132	74,817	19,572
Proceeds from sale of cost method investment in real estate	2,717	0	0
Proceeds from mortgage repayment by previously consolidated VIE	0	35,057	0
Proceeds from mortgages and notes receivable repayments	2,464	14,893	17,797
Net cash used in investing activities	(207,946)	(113,254)	(296,813)
FINANCING ACTIVITIES
Net borrowings (repayments) on unsecured credit facility	128,000	(102,000)	212,000
Borrowings on notes and bonds payable	247,948
Repayments on notes and bonds payable	(19,984)	(4,990)	(3,703)
Repurchase of notes payable	(371,839)		(280,201)
Dividends paid	(111,571)	(96,356)	(89,270)
Net proceeds from issuance of common stock	220,252	202,352	251,916
Common stock redemptions	(454)	(68)	(86)
Capital contributions received from noncontrolling interests	1,806	0	0
Distributions to noncontrolling interest holders	(32)	(40)	(284)
Distributions to noncontrolling interest holders	0	0	(1,591)
Debt issuance and assumption costs	(5,082)	(3)	(8,403)
Net cash provided by (used in) financing activities	89,044	(1,105)	80,378
Increase (decrease) in cash and cash equivalents	1,895	2,038	(108,583)
Cash and cash equivalents, beginning of period	6,776	4,738	113,321
Cash and cash equivalents, end of period	8,671	6,776	4,738
Supplemental Cash Flow Information:
Interest paid	71,025	75,348	73,157
Capitalized interest	183	5,021	8,531
Company-financed real estate property sales	4,241	11,200	2,700
Invoices accrued for construction, tenant improvement and other capitalized costs	10,885	4,297	12,131
Elimination of mortgage note upon acquisition	97,203	0	0
Mortgage notes payable assumed upon acquisition (adjusted to fair value)	40,992	5,171	54,392
Construction liabilities transferred upon deconsolidation of VIE	0	3,450	0
Foreclosure of mortgage notes receivable	0		4,371
Elimination of mortgage note upon consolidation of VIE	$ 0		$ 21,939