Consolidated Statements Of Cash Flows (USD $)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Cash flows from operating activities:
Net income	$ 80,606,000	$ 77,890,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	63,340,000	58,056,000
In-place lease adjustment	643,000	333,000
Tenant improvement reimbursements net of lease incentives	(615,000)	(391,000)
Amortization of mortgage premium	(177,000)	(213,000)
Gain on sale of real estate facility	(2,717,000)	(5,153,000)
Stock compensation	1,202,000	1,652,000
Increase in receivables and other assets	(2,317,000)	(2,968,000)
Increase in accrued and other liabilities	2,593,000	5,875,000
Total adjustments	61,952,000	57,191,000
Net cash provided by operating activities	142,558,000	135,081,000
Cash flows from investing activities:
Capital improvements to real estate facilities	(30,494,000)	(28,386,000)
Acquisition of real estate facilities	(30,060,000)	(158,546,000)
Proceeds from sale of real estate facility	9,183,000	9,181,000
Net cash used in investing activities	(51,371,000)	(177,751,000)
Cash flows from financing activities:
Borrowings on credit facility	146,000,000
Note payable to affiliate	121,000,000
Repayment of borrowings on credit facility	(93,000,000)
Repayment of note payable to affiliate	(121,000,000)
Principal payments on mortgage notes payable	(824,000)	(810,000)
Repayment of mortgage note payable	(2,660,000)
Proceeds from the exercise of stock options	1,050,000	6,382,000
Redemption/repurchase of preferred units	(39,087,000)	(20,000,000)
Redemption of preferred stock		(54,125,000)
Repurchase of common stock	(30,252,000)
Distributions paid to common shareholders	(32,430,000)	(32,398,000)
Distributions paid to preferred shareholders	(31,349,000)	(32,104,000)
Distributions paid to noncontrolling interests -- common units	(9,642,000)	(9,642,000)
Distributions paid to noncontrolling interests - preferred units	(298,000)	(3,536,000)
Net cash used in financing activities	(92,492,000)	(146,233,000)
Net decrease in cash and cash equivalents	(1,305,000)	(188,903,000)
Cash and cash equivalents at the beginning of the period	5,066,000	208,229,000
Cash and cash equivalents at the end of the period	3,761,000	19,326,000
Adjustment to noncontrolling interests in underlying operating partnership:
Noncontrolling interests - common units	5,538,000	964,000
Paid-in capital	(5,538,000)	(964,000)
Gain on repurchase of preferred equity:
Preferred units	(8,748,000)
Paid-in capital	8,748,000
Issuance costs related to the redemption/repurchase of preferred equity:
Cumulative distributions		(1,854,000)
Noncontrolling interest - common units	(1,359,000)	(582,000)
Paid-in capital	$ 1,359,000	$ 2,436,000