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	$ 58,423	$ 33,374	$ 39,093
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	58,014	50,349	52,403
Amortization of deferred financing costs	5,583	4,354	3,877
Non-cash interest expense related to amortization of discount on exchangeable senior notes	1,761	1,664	2,239
Gain on repurchase of exchangeable senior notes			(27,928)
Compensation expense related to stock-based awards	5,757	4,580	3,809
Non-cash unrecovered development and acquisition costs			19,011
Loss on sublease		2,000
Distributions from real estate ventures in excess of earnings	7,008	6,722	5,968
Changes in operating assets and liabilities:
Receivables from related parties and affiliated real estate joint ventures	(8,634)	3,011	(12,347)
Other assets	7,533	(1,676)	(6,584)
Accounts payable and accrued expenses	9,837	1,856	(1,675)
Other liabilities	(1,118)	(1,419)	3,299
Net cash provided by operating activities	144,164	104,815	81,165
Cash flows from investing activities:
Acquisition of real estate assets	(194,959)	(69,588)	(38,185)
Development and construction of real estate assets	(7,060)	(36,062)	(67,301)
Proceeds from sale of real estate assets			4,652
Proceeds from sale of properties to joint venture		15,750
Investments in real estate ventures	(4,088)	(9,699)	(3,246)
Return of investment in real estate ventures	4,614	8,802	1,315
Change in restricted cash	4,730	9,036	(497)
Purchase of affiliated joint venture note receivable, net of principal payments received	(50,140)
Purchase of equipment and fixtures	(5,016)	(1,945)	(1,148)
Net cash used in investing activities	(251,919)	(83,706)	(104,410)
Cash flows from financing activities:
Proceeds from the sale of common stock, net of offering costs	112,349
Repurchase of exchangeable senior notes			(87,734)
Proceeds from notes payable and lines of credit	475,487	191,062	442,560
Principal payments on notes payable and lines of credit	(452,347)	(252,400)	(212,515)
Deferred financing costs	(6,197)	(4,160)	(8,716)
Investments from other noncontrolling interests		87
Redemption of Operating Partnership units held by noncontrolling interest	(271)	(4,116)	(1,908)
Net proceeds from exercise of stock options	18,622	5,661
Dividends paid on common stock	(52,027)	(34,964)	(32,800)
Distributions to noncontrolling interests	(8,127)	(7,479)	(7,664)
Net cash provided by (used in) financing activities	87,489	(106,309)	91,223
Net increase (decrease) in cash and cash equivalents	(20,266)	(85,200)	67,978
Cash and cash equivalents, beginning of the period	46,750	131,950	63,972
Cash and cash equivalents, end of the period	26,484	46,750	131,950
Supplemental schedule of cash flow information
Interest paid, net of amounts capitalized	61,726	60,100	64,175
Income taxes paid	665	6,539	4,292
Deconsolidation of joint ventures due to application of Accounting Standards Codification 810:
Real estate assets, net		(42,739)
Investments in real estate ventures		404
Receivables from related parties and affiliated real estate joint ventures		21,142
Other assets and other liabilities		(51)
Notes payable		21,348
Other noncontrolling interests		(104)
Redemption of Operating Partnership units held by noncontrolling interests for common stock:
Noncontrolling interests in Operating Partnership	2,344		3,583
Common stock and paid-in capital	(2,344)		(3,583)
Tax effect from vesting of restricted stock grants and stock option exercises
Other assets	2,199	836	(414)
Paid-in capital	(2,199)	(836)	414
Acquisitions of real estate assets
Real estate assets, net	137,177	25,963
Notes payable assumed	(132,327)	(25,963)
Notes payable issued to seller	4,850
Change in receivables from related parties and affiliated real estate joint ventures due to consolidation of joint venture properties			$ 18,568