Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income	$ 47,664	$ 26,318	$ 47,078
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	148,630	132,215	123,148
Amortization of senior note debt discount	1,782	2,082	1,967
Accreted debt discount on repurchase of exchangeable senior notes	(9,765)
Loss (gain) on disposition of property		13	(24,314)
Stock-based compensation	10,105	7,647	7,291
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	813	(4,087)	1,359
Other assets	(296)	(2,823)	(372)
Accounts payable and accrued liabilities	(1,228)	382	(6,533)
Total adjustments	150,041	133,701	102,546
Net cash provided by operating activities	197,705	160,019	149,624
Cash flows from investing activities:
Purchase of properties, net of mortgage notes assumed and UPREIT Units issued	(498,558)	(186,284)
Purchase of land for development	(12,750)
Additions to properties	(126,786)	(97,590)	(79,292)
Additions to construction in progress	(32,038)	(45,981)	(73,627)
Additions to predevelopment	(1,310)
Proceeds from (payments for) sale of properties, net	5,426	(13)	105,930
Proceeds from notes receivable	1,015
Purchase of notes receivable		(1,433)
Withdrawals from (additions to) cash held in escrow, net	658	(3,238)	(576)
Net cash used in investing activities	(664,343)	(334,539)	(47,565)
Cash flows from financing activities:
Proceeds from sale of common stock, net	216,603	123,756	46,648
Proceeds from issuance of common stock through public offering, net	336,760
Repurchase of common stock	(5,770)	(3,274)	(2,935)
Proceeds from mortgage notes payable		628,154	266,483
Payments of mortgage notes payable	(163,395)	(456,192)	(264,248)
Proceeds from unsecured notes payable	400,000
Payment for repurchase of exchangeable senior notes	(130,235)
Proceeds from unsecured line of credit	522,000	449,000	481,500
Payments on unsecured line of credit	(576,000)	(446,000)	(499,000)
Proceeds from unsecured term loan	135,000
Payments on unsecured term loan	(135,000)
Payments of deferred loan costs, net	(4,953)	(6,324)	(6,592)
Additions to cash escrows, net	(5)	(395)	(133)
Dividends and distributions paid	(130,852)	(112,232)	(121,540)
Net cash provided by (used in) financing activities	464,153	176,493	(99,817)
Net increase (decrease) in cash and cash equivalents	(2,485)	1,973	2,242
Cash and cash equivalents:
Beginning of year	10,782	8,809	6,567
End of year	$ 8,297	$ 10,782	$ 8,809