Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net income/(loss)	$ 159,842	$ 46,282	$ 220,303
Deprecation and Amortization, Including Discontinued Operations	363,929	348,231	354,505
Gain Loss on the Sale of Real Estate, Including Discontinued Operations	143,647	41,919	251,554
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Impairment loss, net of tax	0	1,470	0
Tax benefit/(provision), net	(15,136)	(7,299)	(30,282)
Loss from unconsolidated entities	7,006	415	8,579
Casualty-related (recoveries)/charges, net	541	(270)	8,495
Other	26,517	24,826	26,009
Changes in operating assets and liabilities:
Increase/(decrease) in operating assets	(1,074)	(15,135)	12,647
Increase/(decrease) in operating liabilites	(5,618)	(16,699)	(21,515)
Net cash provided by operating activities	392,360	339,902	327,187
Investing Activities
Acquisition of real estate assets (net of liabilities assumed) and initial capital expenditures	(228,810)	0	(108,215)
Proceeds from sales of real estate investments, net	383,886	250,043	593,167
Development of real estate assets	(251,493)	(280,603)	(246,923)
Capital expenditures and other major improvements - real estate assets, net of escrow reimbursement	(96,679)	(153,676)	(144,877)
Capital expenditures - non-real estate assets	(5,497)	(7,639)	(7,947)
Investment in unconsolidated joint ventures	(222,930)	(43,291)	(283,369)
Distributions received from unconsolidated joint venture	59,199	130,984	50,580
(Issuance)/repayment of notes receivable	68,664	(19,027)	(63,998)
Net cash provided by/(used in) investing activities	(293,660)	(123,209)	(211,582)
Financing Activities
Payments on secured debt	(80,961)	(46,564)	(491,885)
Proceeds from the issuance of secured debt	5,502	0	250
Payments on unsecured debt	(312,500)	(122,500)	(100,000)
Proceeds from the issuance of unsecured debt	298,956	299,943	396,400
Net (repayment)/borrowings of revolving bank debt	152,500	(76,000)	(345,000)
Proceeds from the issuance of common shares through public offering, net	99,849	0	756,138
Payments from the repurchase of Series G preferred stock, net	0	0	(81,609)
Distributions paid to non-controlling interests	(9,929)	(9,348)	(9,033)
Acquisition of nonredeemable noncontrolling interests	0	0	(4,871)
Distributions paid to preferred stockholders	(3,724)	(3,724)	(6,954)
Distributions paid to common stockholders	(256,100)	(231,822)	(207,470)
Other	(7,318)	(8,544)	(21,959)
Net cash (used in)/provided by financing activities	(113,725)	(198,559)	(115,993)
Net increase in cash and cash equivalents	(15,025)	18,134	(388)
Cash and cash equivalents, beginning of period	30,249	12,115	12,503
Cash and cash equivalents, end of period	15,224	30,249	12,115
Supplemental Information:
Interest paid during the period, net of amounts capitalized	131,815	127,877	133,133
Non-cash transactions:
Real estate acquired in asset exchange or upon consolidation of joint ventures	0	129,437	0
Transfer of real estate owned to investment in and advances to unconsolidated ventures	54,938	175,951
Secured debt assumed in the acquisitions of properties, including asset exchange	0	63,595	34,412
Fair market value adjustment of secured debt assumed in acquisitions of properties, including asset exchange	0	0	2,617
Development costs and capital expenditures incurred but not yet paid	34,746	37,220	24,551
Contribution of purchase deposit made in 2011 to unconsolidated joint venture	0	0	80,397
Conversion of operating partnership non-controlling interests to common stock (18,440 shares in 2012 and 4,453 shares in 2011)	4,372	1,817	529
Unconsolidated Joint Venture Vitruvian Park [Member]
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Loss from unconsolidated entities	4,068	2,851	0
Non-cash transactions:
Transfer of real estate owned to investment in and advances to unconsolidated ventures			$ 0