Consolidated Statements Of Cash Flows (USD $)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 62,949,000	$ 55,207,000
Adjustments to reconcile net income to net cash provided by Operating activities:
Depreciation and amortization, including related intangible assets	144,481,000	143,124,000
Depreciation and amortization on discontinued operations		409,000
Amortization of stock compensation	2,393,000	2,173,000
Amortization of deferred financing costs and debt discount	1,752,000	2,021,000
Equity in earnings of unconsolidated joint venture, net	(1,174,000)	(213,000)
Realized gains on disposition of rental property		(4,447,000)
Distributions of cumulative earnings from unconsolidated joint ventures	2,482,000	313,000
Changes in operating assets and liabilities:
Increase in unbilled rents receivable, net	(4,927,000)	(5,034,000)
Increase in deferred charges and other assets, net	(31,238,000)	(22,964,000)
Decrease (increase) in accounts receivable, net	3,779,000	(6,602,000)
Increase in accounts payable, accrued expenses and other liabilities	5,928,000	3,376,000
Decrease in rents received in advance and security deposits	(5,653,000)	(4,980,000)
Decrease in accrued interest payable	(10,163,000)	(18,429,000)
Net cash provided by operating activities	170,609,000	143,954,000
CASH FLOWS FROM INVESTING ACTIVITIES
Additions to rental property and related intangibles	(65,230,000)	(47,175,000)
Investment in unconsolidated joint ventures	(334,000)	(833,000)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	1,280,000	438,000
(Increase) decrease in restricted cash	(2,321,000)	1,292,000
Net cash used in investing activities	(66,605,000)	(46,278,000)
CASH FLOW FROM FINANCING ACTIVITIES
Borrowings from revolving credit facility	219,000,000
Repayment of revolving credit facility	(420,000,000)
Repayment of senior unsecured notes		(150,000,000)
Proceeds from offering of common stock	227,374,000
Repayment of mortgages, loans payable and other obligations	(6,382,000)	(6,032,000)
Payment of financing costs	(14,000)	(2,010,000)
Proceeds from stock options exercised	3,048,000	1,473,000
Payment of dividends and distributions	(133,027,000)	(126,354,000)
Net cash used in financing activities	(110,001,000)	(282,923,000)
Net decrease in cash and cash equivalents	(5,997,000)	(185,247,000)
Cash and cash equivalents, beginning of period	21,851,000	291,059,000
Cash and cash equivalents, end of period	$ 15,854,000	$ 105,812,000