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	$ 163,622	$ 47,664	$ 26,318
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	172,558	148,630	132,215
Amortization of senior note debt discount		1,782	2,082
Accreted debt discount on repurchase of exchangeable senior notes		(9,765)
Loss (gain) on disposition of property	(80,532)		13
Stock-based compensation	13,923	10,105	7,647
Carrying amount of assets and liabilities disposed in connection with sale of general partnership interest			(1,728)
Changes in assets and liabilities:
Cash in escrows, net	1,881	813	(4,087)
Other assets	(8,250)	(296)	(2,823)
Accounts payable and accrued liabilities	4,378	(1,228)	382
Total adjustments	103,958	150,041	133,701
Net cash provided by operating activities	267,580	197,705	160,019
Cash flows from investing activities:
Purchase of properties, net of mortgage notes assumed and UPREIT Units issued	(289,759)	(498,558)	(186,284)
Purchase of land for development		(12,750)
Capital improvements to properties including redevelopment	(164,987)	(126,786)	(97,590)
Additions to construction in progress	(61,806)	(32,038)	(45,981)
Additions to predevelopment	(535)	(1,310)
Proceeds from (payments for) sale of properties, net	149,783	5,426	(13)
Proceeds from notes receivable		1,015
Purchase of notes receivable			(1,433)
Withdrawals from (additions to) cash held in escrow, net	1,301	658	(3,238)
Net cash used in investing activities	(366,003)	(664,343)	(334,539)
Cash flows from financing activities:
Proceeds from sale of common stock, net	165,968	216,603	123,756
Proceeds from issuance of common stock through public offering, net		336,760
Repurchase of common stock	(4,245)	(5,770)	(3,274)
Proceeds from mortgage notes payable			628,154
Payments of mortgage notes payable	(103,197)	(163,395)	(456,192)
Proceeds from unsecured notes payable	150,000	400,000
Payments on unsecured notes payable	(100,000)
Payment for repurchase of exchangeable senior notes		(130,235)
Proceeds from unsecured line of credit	524,000	522,000	449,000
Payments on unsecured line of credit	(364,000)	(576,000)	(446,000)
Proceeds from unsecured term loan		135,000
Payments on unsecured term loan		(135,000)
Payments of deferred loan costs, net	(410)	(4,953)	(6,324)
Withdrawals from (additions to) cash held in escrow, net	2,451	(5)	(395)
Dividends and distributions paid	(159,349)	(130,852)	(112,232)
Net cash provided by financing activities	111,218	464,153	176,493
Net increase (decrease) in cash and cash equivalents	12,795	(2,485)	1,973
Cash and cash equivalents:
Beginning of year	8,297	10,782	8,809
End of year	$ 21,092	$ 8,297	$ 10,782