CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 159,152	$ 157,032	$ 130,784
Adjustments to net income:
Depreciation and amortization	149,597	118,874	91,641
Income from discontinued operations	(13,181)	(12,407)	(15,583)
Gain on sale of real estate		(540)
Amortization of share-based compensation	10,001	7,873	6,166
Amortization of net premiums on mortgages payable	(665)	(189)
Provisions for impairment on real estate held for investment	2,804	10	849
Other non-cash adjustments	(301)
Cash provided by discontinued operations:
Real estate	7,353	10,914	11,586
Collection of notes receivable by Crest	90	3,032	138
Changes in assets and liabilities:
Accounts receivable and other assets	2,775	5,209	5,270
Accounts payable, accrued expenses and other liabilities	8,844	9,144	12,517
Net cash provided by operating activities	326,469	298,952	243,368
CASH FLOWS FROM INVESTING ACTIVITIES
Acquisition of investment properties	(1,015,725)	(953,175)	(713,198)
Improvements to real estate, including leasing costs	(6,554)	(4,172)	(3,578)
Loans receivable	(34,876)	(1,593)
Proceeds from sales of real estate:
Continuing operations	23	2,078
Discontinued operations	50,563	22,049	25,779
Restricted escrow deposits	(1,805)	(50)	(6,361)
Net cash used in investing activities	(1,008,374)	(934,863)	(697,358)
CASH FLOWS FROM FINANCING ACTIVITIES
Cash distributions to common stockholders	(236,348)	(219,297)	(182,500)
Cash dividends to preferred stockholders	(39,445)	(24,253)	(24,253)
Borrowings on lines of credit	1,074,000	612,800	612,200
Payments on lines of credit	(1,153,400)	(375,400)	(616,800)
Principal payments on mortgages	(11,729)	(279)
Proceeds from preferred stock offerings, net	395,377
Redemption of preferred stock	(127,500)
Proceeds from common stock offerings, net		489,236	432,591
Proceeds from bonds issued	800,000	150,000
Proceeds from notes payable issued, net			246,131
Debt issuance costs	(16,979)	(9,864)	(4,091)
Proceeds from dividend reinvestment and stock purchase plan, net	2,159	1,894
Other items	(3,147)	(2,368)	(1,707)
Net cash provided by financing activities	682,988	622,469	461,571
Net increase (decrease) in cash and cash equivalents	1,083	(13,442)	7,581
Cash and cash equivalents, beginning of year	4,165	17,607	10,026
Cash and cash equivalents, end of year	$ 5,248	$ 4,165	$ 17,607