Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Document Fiscal Year Focus	2014
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in income of investments in real estate partnerships (note 4)	$ (31,270)	$ (31,718)	$ (23,807)
Deferred income tax expense (benefit) of taxable REIT subsidiary	0	0	13,727
Cash flows from investing activities:
Proceeds from sale of real estate investments	118,787	212,632	352,707
Parent Company [Member]
Cash flows from operating activities:
Net income	188,847	151,285	26,209
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	147,791	134,454	127,839
Amortization of deferred loan cost and debt premium	10,521	12,339	12,759
Amortization and (accretion) of above and below market lease intangibles, net	(3,101)	(2,488)	(1,043)
Stock-based compensation, net of capitalization	9,662	12,191	9,806
Equity in income of investments in real estate partnerships (note 4)	(31,270)	(31,718)	(23,807)
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	18,271	0	0
Gain on sale of real estate, net of tax	(55,077)	(59,656)	(24,013)
Provision for impairment	1,257	6,000	74,816
Early extinguishment of debt	18	32	852
Deferred income tax expense (benefit) of taxable REIT subsidiary	0	0	13,727
Distribution of earnings from operations of investments in real estate partnerships	42,767	45,377	44,809
Loss on settlement of derivative instruments	4,648	0	0
(Gain) on derivative instruments	(13)	(19)	(22)
Deferred compensation expense	1,386	3,294	2,069
Realized and unrealized (gain) loss on investments (note 8 and 14)	(9,158)	(3,293)	(2,095)
Changes in assets and liabilities:
Restricted cash	848	(62)	(423)
Accounts receivable	(6,225)	(5,042)	6,157
Straight-line rent receivable, net	(6,544)	(5,459)	(6,059)
Deferred leasing costs	(8,252)	(10,086)	(12,642)
Other assets	89	(1,866)	(1,079)
Accounts payable and other liabilities	6,201	(672)	10,994
Tenants’ security and escrow deposits and prepaid rent	1,618	6,120	(1,639)
Net cash provided by operating activities	277,742	250,731	257,215
Cash flows from investing activities:
Acquisition of operating real estate	(112,120)	(107,790)	(156,026)
Real estate development and capital improvements	(238,237)	(213,282)	(164,588)
Proceeds from sale of real estate investments	118,787	212,632	352,707
Collection (issuance) of notes receivable	0	27,354	(552)
Investments in real estate partnerships (note 4)	(23,577)	(10,883)	(66,663)
Distributions received from investments in real estate partnerships	37,152	87,111	38,353
Dividends on investments	243	194	245
Acquisition of securities	(23,760)	(19,144)	(17,930)
Proceeds from sale of securities	31,222	13,991	18,077
Net cash (used in) provided by investing activities	(210,290)	(9,817)	3,623
Cash flows from financing activities:
Net proceeds from issuance of preferred stock	0	0	313,900
Stock Issued During Period, Value, New Issues	102,453	99,753	21,542
Proceeds from sale of treasury stock	0	34	338
Payments for Acquisiton of Treasury Stock	0	0	(4)
Redemption of preferred stock and partnership units	(300)	0	(323,125)
Payments to Noncontrolling Interests	(5,303)	1,514	1,375
Payments of Ordinary Dividends, Noncontrolling Interest	(300)	(322)	(324)
Payments of Preferred Dividends, Noncontrolling Interest	0	0	(404)
Dividends paid to common stockholders	(172,600)	(167,773)	(164,423)
Dividends paid to preferred stockholders	(21,062)	(21,062)	(23,254)
Dividends, Preferred Stock, Cash	21,062	21,062	23,658
Repayment of fixed rate unsecured notes	(150,000)	0	(192,377)
Proceeds from Issuance of Unsecured Debt	248,705	0	0
Proceeds from unsecured credit facilities	255,000	82,000	750,000
Repayment of unsecured credit facilities	(255,000)	(177,000)	(620,000)
Proceeds from notes payable	12,739	36,350	0
Repayment of notes payable	(38,717)	(27,960)	(1,332)
Scheduled principal payments	(6,909)	(7,530)	(7,259)
Payment of loan costs	(3,066)	(583)	(4,544)
Net cash used in financing activities	(34,360)	(182,579)	(249,891)
Net increase in cash and cash equivalents	33,092	58,335	10,947
Cash and cash equivalents at beginning of the period	80,684	22,349	11,402
Cash and cash equivalents at end of the period	113,776	80,684	22,349
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $000, $6,078, and $3,686 in 2014, 2013, and 2012, respectively)	109,425	107,312	115,879
Income Taxes Paid	2,169	0	0
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed through distribution in kind	0	7,500	0
Stock Issued During Period, Value, Conversion of Units	137	302	0
Real estate received through distribution in kind	0	7,576	0
Mortgage loans assumed for the acquisition of real estate	103,187	0	30,467
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value	15,385	0	0
Real estate contributed for investments in real estate partnerships	0	0	47,500
Real estate received through foreclosure on notes receivable	0	0	12,585
Acquisition of previously unconsolidated real estate	16,182	0	0
Change in fair value of derivative instruments	(49,968)	30,952	(4,285)
Contributions from limited partners in consolidated partnerships, net	1,579	156	986
Common stock issued for dividend reinvestment in trust	779	660	440
Common stock issued for dividend reinvestment plan	1,184	1,075	988
Stock-based compensation capitalized	2,707	2,188	1,979
Contribution of stock awards into trust	1,881	1,537	819
Distribution of stock held in trust	4	201	1,191
Partnership Interest [Member]
Cash flows from operating activities:
Net income	188,847	151,285	26,209
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	147,791	134,454	127,839
Amortization of deferred loan cost and debt premium	10,521	12,339	12,759
Amortization and (accretion) of above and below market lease intangibles, net	(3,101)	(2,488)	(1,043)
Stock-based compensation, net of capitalization	9,662	12,191	9,806
Equity in income of investments in real estate partnerships (note 4)	(31,270)	(31,718)	(23,807)
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	18,271	0	0
Gain on sale of real estate, net of tax	(55,077)	(59,656)	(24,013)
Provision for impairment	1,257	6,000	74,816
Early extinguishment of debt	18	32	852
Deferred income tax expense (benefit) of taxable REIT subsidiary	0	0	13,727
Distribution of earnings from operations of investments in real estate partnerships	42,767	45,377	44,809
Loss on settlement of derivative instruments	4,648	0	0
(Gain) on derivative instruments	(13)	(19)	(22)
Deferred compensation expense	1,386	3,294	2,069
Realized and unrealized (gain) loss on investments (note 8 and 14)	(9,158)	(3,293)	(2,095)
Changes in assets and liabilities:
Restricted cash	848	(62)	(423)
Accounts receivable	(6,225)	(5,042)	6,157
Straight-line rent receivable, net	(6,544)	(5,459)	(6,059)
Deferred leasing costs	(8,252)	(10,086)	(12,642)
Other assets	89	(1,866)	(1,079)
Accounts payable and other liabilities	6,201	(672)	10,994
Tenants’ security and escrow deposits and prepaid rent	1,618	6,120	(1,639)
Net cash provided by operating activities	277,742	250,731	257,215
Cash flows from investing activities:
Acquisition of operating real estate	(112,120)	(107,790)	(156,026)
Real estate development and capital improvements	(238,237)	(213,282)	(164,588)
Proceeds from sale of real estate investments	118,787	212,632	352,707
Collection (issuance) of notes receivable	0	27,354	(552)
Investments in real estate partnerships (note 4)	(23,577)	(10,883)	(66,663)
Distributions received from investments in real estate partnerships	37,152	87,111	38,353
Dividends on investments	243	194	245
Acquisition of securities	(23,760)	(19,144)	(17,930)
Proceeds from sale of securities	31,222	13,991	18,077
Net cash (used in) provided by investing activities	(210,290)	(9,817)	3,623
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	102,453	99,753	21,542
Net proceeds from issuance of preferred stock	0	0	313,900
Stock Issued During Period, Value, New Issues			(313,900)
Proceeds from sale of treasury stock	0	34	338
Payments for Acquisiton of Treasury Stock	0	0	(4)
Redemption of preferred stock and partnership units	(300)	0	(323,125)
Payments to Noncontrolling Interests	(5,303)	1,514	1,375
Dividends paid to common stockholders	(172,900)	(168,095)	(164,747)
Dividends paid to preferred stockholders	(21,062)	(21,062)	(23,658)
Dividends, Preferred Stock, Cash	(21,062)	(21,062)	(23,658)
Repayment of fixed rate unsecured notes	(150,000)	0	(192,377)
Proceeds from Issuance of Unsecured Debt	248,705	0	0
Proceeds from unsecured credit facilities	255,000	82,000	750,000
Repayment of unsecured credit facilities	(255,000)	(177,000)	(620,000)
Proceeds from notes payable	12,739	36,350	0
Repayment of notes payable	(38,717)	(27,960)	(1,332)
Scheduled principal payments	(6,909)	(7,530)	(7,259)
Payment of loan costs	(3,066)	(583)	(4,544)
Net cash used in financing activities	(34,360)	(182,579)	(249,891)
Net increase in cash and cash equivalents	33,092	58,335	10,947
Cash and cash equivalents at beginning of the period	80,684	22,349	11,402
Cash and cash equivalents at end of the period	113,776	80,684	22,349
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $000, $6,078, and $3,686 in 2014, 2013, and 2012, respectively)	109,425	107,312	115,879
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed through distribution in kind	0	7,500	0
Stock Issued During Period, Value, Conversion of Units	137	302	0
Real estate received through distribution in kind	0	7,576	0
Mortgage loans assumed for the acquisition of real estate	103,187	0	30,467
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value	15,385	0	0
Real estate contributed for investments in real estate partnerships	0	0	47,500
Real estate received through foreclosure on notes receivable	0	0	12,585
Acquisition of previously unconsolidated real estate	16,182	0	0
Change in fair value of derivative instruments	(49,968)	30,952	(4,285)
Contributions from limited partners in consolidated partnerships, net	1,579	156	986
Common stock issued for dividend reinvestment in trust	779	660	440
Common stock issued for dividend reinvestment plan	1,184	1,075	988
Stock-based compensation capitalized	2,707	2,188	1,979
Contribution of stock awards into trust	1,881	1,537	819
Distribution of stock held in trust	4	201	1,191
Common Stock | Parent Company [Member]
Cash flows from financing activities:
Stock Issued During Period, Value, New Issues	(102,453)	(99,753)
Supplemental disclosure of non-cash transactions:
Stock Issued During Period, Value, Conversion of Units	$ 0	$ 0