Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Document Fiscal Year Focus	2013
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in income of investments in real estate partnerships (note 4)	$ (31,718,000)	$ (23,807,000)	$ (9,643,000)
Net gain on sale of properties	(59,656,000)	(24,013,000)	(8,346,000)
Deferred income tax expense (benefit) of taxable REIT subsidiary	0	13,727,000	2,422,000
Cash flows from investing activities:
Proceeds from sale of real estate investments	212,632,000	352,707,000	86,233,000
Partnership [Member]
Cash flows from operating activities:
Net income	151,285,000	26,209,000	55,788,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	134,454,000	127,839,000	133,756,000
Amortization of deferred loan cost and debt premium	12,339,000	12,759,000	12,327,000
Amortization and (accretion) of above and below market lease intangibles, net	(2,488,000)	(1,043,000)	(931,000)
Stock-based compensation, net of capitalization	12,191,000	9,806,000	9,824,000
Equity in income of investments in real estate partnerships (note 4)	(31,718,000)	(23,807,000)	(9,643,000)
Net gain on sale of properties	(59,656,000)	(24,013,000)	(8,346,000)
Provision for impairment	6,000,000	74,816,000	15,883,000
Early extinguishment of debt	32,000	852,000	0
Deferred income tax expense (benefit) of taxable REIT subsidiary	0	13,727,000	2,422,000
Distribution of earnings from operations of investments in real estate partnerships	45,377,000	44,809,000	43,361,000
Loss on settlement of derivative instruments	0	0	0
(Gain) loss on derivative instruments	(19,000)	(22,000)	54,000
Deferred compensation expense (income)	3,294,000	2,069,000	(2,136,000)
Realized and unrealized (gain) loss on trading securities held in trust (note 13)	(3,293,000)	(2,095,000)	184,000
Changes in assets and liabilities:
Restricted cash	(62,000)	(423,000)	(651,000)
Accounts receivable	(5,042,000)	6,157,000	(3,108,000)
Straight-line rent receivable, net	(5,459,000)	(6,059,000)	(4,642,000)
Deferred leasing costs	(10,086,000)	(12,642,000)	(15,013,000)
Other assets (note 9)	(1,866,000)	(1,079,000)	(3,393,000)
Accounts payable and other liabilities (note 9 and 13)	(672,000)	10,994,000	(17,892,000)
Tenants’ security and escrow deposits and prepaid rent	6,120,000	(1,639,000)	9,789,000
Net cash provided by operating activities	250,731,000	257,215,000	217,633,000
Cash flows from investing activities:
Acquisition of operating real estate	(107,790,000)	(156,026,000)	(70,629,000)
Real estate development and capital improvements	(213,282,000)	(164,588,000)	(82,069,000)
Proceeds from sale of real estate investments	212,632,000	352,707,000	86,233,000
Collection (issuance) of notes receivable	27,354,000	(552,000)	(78,000)
Investments in real estate partnerships (note 4)	(10,883,000)	(66,663,000)	(198,688,000)
Distributions received from investments in real estate partnerships	87,111,000	38,353,000	188,514,000
Dividends on trading securities held in trust	194,000	245,000	225,000
Acquisition of securities	(19,144,000)	(17,930,000)	(19,377,000)
Proceeds from sale securities	13,991,000	18,077,000	18,146,000
Net cash (used in) provided by investing activities	(9,817,000)	3,623,000	(77,723,000)
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	99,753,000	21,542,000	215,369,000
Net proceeds from issuance of preferred stock	0	313,900,000	0
Proceeds from sale of treasury stock	34,000	338,000	2,128,000
Payments for Acquisiton of Treasury Stock	0	(4,000)	(13,000)
Redemption of preferred stock and partnership units	0	(323,125,000)	0
Payments to Noncontrolling Interests	(1,514,000)	(1,375,000)	735,000
Dividends paid to common stockholders	(168,095,000)	(164,747,000)	(160,479,000)
Dividends paid to preferred stockholders	(21,062,000)	(23,658,000)	(23,400,000)
Repayment of fixed rate unsecured notes	0	(192,377,000)	(181,691,000)
Proceeds from unsecured credit facilities	82,000,000	750,000,000	455,000,000
Repayment of unsecured credit facilities	(177,000,000)	(620,000,000)	(425,000,000)
Proceeds from notes payable	36,350,000	0	1,940,000
Repayment of notes payable	(27,960,000)	(1,332,000)	(16,919,000)
Scheduled principal payments	(7,530,000)	(7,259,000)	(5,699,000)
Payment of loan costs	(583,000)	(4,544,000)	(6,070,000)
Net cash used in financing activities	(182,579,000)	(249,891,000)	(145,569,000)
Net increase (decrease) in cash and cash equivalents	58,335,000	10,947,000	(5,659,000)
Cash and cash equivalents at beginning of the period	22,349,000	11,402,000	17,061,000
Cash and cash equivalents at end of the period	80,684,000	22,349,000	11,402,000
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $6,078, $3,686, and $1,480 in 2013, 2012, and 2011, respectively)	107,312,000	115,879,000	128,649,000
Supplemental disclosure of non-cash transactions:
Common stock issued for partnership units exchanged	302,000	0	0
Real estate received through distribution in kind	7,576,000	0	47,512,000
Mortgage loans assumed through distribution in kind	7,500,000	0	28,760,000
Mortgage loans assumed for the acquisition of real estate	0	30,467,000	31,292,000
Real estate contributed for investments in real estate partnerships	0	47,500,000	0
Real estate received through foreclosure on notes receivable	0	12,585,000	0
Change in fair value of derivative instruments	30,952,000	(4,285,000)	18,000
Contributions from limited partners in consolidated partnerships, net	156,000	986,000	2,411,000
Common stock issued for dividend reinvestment in trust	660,000	440,000	631,000
Common stock issued for dividend reinvestment plan	1,075,000	988,000	1,081,000
Stock-based compensation capitalized	2,188,000	1,979,000	1,104,000
Contribution of stock awards into trust	1,537,000	819,000	1,132,000
Distribution of stock held in trust	201,000	1,191,000	0
Parent Company [Member]
Cash flows from operating activities:
Net income	151,285,000	26,209,000	55,788,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	134,454,000	127,839,000	133,756,000
Amortization of deferred loan cost and debt premium	12,339,000	12,759,000	12,327,000
Amortization and (accretion) of above and below market lease intangibles, net	(2,488,000)	(1,043,000)	(931,000)
Stock-based compensation, net of capitalization	12,191,000	9,806,000	9,824,000
Equity in income of investments in real estate partnerships (note 4)	(31,718,000)	(23,807,000)	(9,643,000)
Net gain on sale of properties	(59,656,000)	(24,013,000)	(8,346,000)
Provision for impairment	6,000,000	74,816,000	15,883,000
Early extinguishment of debt	32,000	852,000	0
Deferred income tax expense (benefit) of taxable REIT subsidiary	0	13,727,000	2,422,000
Distribution of earnings from operations of investments in real estate partnerships	45,377,000	44,809,000	43,361,000
(Gain) loss on derivative instruments	(19,000)	(22,000)	54,000
Deferred compensation expense (income)	3,294,000	2,069,000	(2,136,000)
Realized and unrealized (gain) loss on trading securities held in trust (note 13)	(3,293,000)	(2,095,000)	184,000
Changes in assets and liabilities:
Restricted cash	(62,000)	(423,000)	(651,000)
Accounts receivable	(5,042,000)	6,157,000	(3,108,000)
Straight-line rent receivable, net	(5,459,000)	(6,059,000)	(4,642,000)
Deferred leasing costs	(10,086,000)	(12,642,000)	(15,013,000)
Other assets (note 9)	(1,866,000)	(1,079,000)	(3,393,000)
Accounts payable and other liabilities (note 9 and 13)	(672,000)	10,994,000	(17,892,000)
Tenants’ security and escrow deposits and prepaid rent	6,120,000	(1,639,000)	9,789,000
Net cash provided by operating activities	250,731,000	257,215,000	217,633,000
Cash flows from investing activities:
Acquisition of operating real estate	(107,790,000)	(156,026,000)	(70,629,000)
Real estate development and capital improvements	(213,282,000)	(164,588,000)	(82,069,000)
Proceeds from sale of real estate investments	212,632,000	352,707,000	86,233,000
Collection (issuance) of notes receivable	27,354,000	(552,000)	(78,000)
Investments in real estate partnerships (note 4)	(10,883,000)	(66,663,000)	(198,688,000)
Distributions received from investments in real estate partnerships	87,111,000	38,353,000	188,514,000
Dividends on trading securities held in trust	194,000	245,000	225,000
Acquisition of securities	(19,144,000)	(17,930,000)	(19,377,000)
Proceeds from sale securities	13,991,000	18,077,000	18,146,000
Net cash (used in) provided by investing activities	(9,817,000)	3,623,000	(77,723,000)
Cash flows from financing activities:
Stock Issued During Period, Value, Other			215,369,000
Stock Issued During Period, Value, New Issues	99,753,000	21,542,000
Net proceeds from issuance of preferred stock	0	313,900,000	0
Proceeds from sale of treasury stock	34,000	338,000	2,128,000
Payments for Acquisiton of Treasury Stock	0	(4,000)	(13,000)
Redemption of preferred stock and partnership units	0	(323,125,000)	0
Payments to Noncontrolling Interests	(1,514,000)	(1,375,000)	735,000
Payments of Ordinary Dividends, Noncontrolling Interest	(322,000)	(324,000)	(324,000)
Payments of Preferred Dividends, Noncontrolling Interest	0	(404,000)	(3,725,000)
Dividends paid to common stockholders	(167,773,000)	(164,423,000)	(160,155,000)
Dividends paid to preferred stockholders	(21,062,000)	(23,254,000)	(19,675,000)
Dividends, Preferred Stock, Cash	21,062,000	23,658,000	23,400,000
Repayment of fixed rate unsecured notes	0	(192,377,000)	(181,691,000)
Proceeds from unsecured credit facilities	82,000,000	750,000,000	455,000,000
Repayment of unsecured credit facilities	(177,000,000)	(620,000,000)	(425,000,000)
Proceeds from notes payable	36,350,000	0	1,940,000
Repayment of notes payable	(27,960,000)	(1,332,000)	(16,919,000)
Scheduled principal payments	(7,530,000)	(7,259,000)	(5,699,000)
Payment of loan costs	(583,000)	(4,544,000)	(6,070,000)
Net cash used in financing activities	(182,579,000)	(249,891,000)	(145,569,000)
Net increase (decrease) in cash and cash equivalents	58,335,000	10,947,000	(5,659,000)
Cash and cash equivalents at beginning of the period	22,349,000	11,402,000	17,061,000
Cash and cash equivalents at end of the period	80,684,000	22,349,000	11,402,000
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $6,078, $3,686, and $1,480 in 2013, 2012, and 2011, respectively)	107,312,000	115,879,000	128,649,000
Supplemental disclosure of non-cash transactions:
Common stock issued for partnership units exchanged	302,000	0	0
Real estate received through distribution in kind	7,576,000	0	47,512,000
Mortgage loans assumed through distribution in kind	7,500,000	0	28,760,000
Mortgage loans assumed for the acquisition of real estate	0	30,467,000	31,292,000
Real estate contributed for investments in real estate partnerships	0	47,500,000	0
Real estate received through foreclosure on notes receivable	0	12,585,000	0
Change in fair value of derivative instruments	30,952,000	(4,285,000)	18,000
Contributions from limited partners in consolidated partnerships, net	156,000	986,000	2,411,000
Common stock issued for dividend reinvestment in trust	660,000	440,000	631,000
Stock-based compensation capitalized	2,188,000	1,979,000	1,104,000
Contribution of stock awards into trust	1,537,000	819,000	1,132,000
Distribution of stock held in trust	201,000	1,191,000	0
Partnership Interest [Member]
Cash flows from operating activities:
Net income	151,285,000	26,209,000	55,788,000
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in income of investments in real estate partnerships (note 4)	(31,718,000)	(23,807,000)	(9,643,000)
Early extinguishment of debt	32,000	852,000	0
Cash flows from financing activities:
Stock Issued During Period, Value, New Issues	0	(313,900,000)
Cash and cash equivalents at beginning of the period	22,349,000
Cash and cash equivalents at end of the period	80,684,000	22,349,000
Common Stock | Parent Company [Member]
Cash flows from financing activities:
Stock Issued During Period, Value, New Issues	(99,753,000)	(21,542,000)
Supplemental disclosure of non-cash transactions:
Common stock issued for partnership units exchanged	0
Common stock issued for dividend reinvestment plan	$ 1,075,000	$ 988,000	$ 1,081,000