Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation, net of capitalization	$ 9,227	$ 7,331
Cash flows from investing activities:
Proceeds from Issuance of Common Stock	101,342
Parent Company [Member]
Cash flows from operating activities:
Net income	99,268	57,903
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	98,620	96,217
Amortization of deferred loan cost and debt premium	9,265	9,619
Accretion of above and below market lease intangibles, net	(1,646)	(667)
Stock-based compensation, net of capitalization	9,227	7,332
Equity in income of investments in real estate partnerships	(25,150)	(19,173)
Net gain on sale of properties	(29,235)	(10,646)
Provision for impairment	(6,000)	(24,655)
Gains (Losses) on Extinguishment of Debt	0	852
Distribution of earnings from operations of investments in real estate partnerships	(34,772)	(28,550)
Loss on derivative instruments	(14)	(17)
Deferred compensation expense	2,023	1,840
Realized and unrealized gains on trading securities held in trust	(2,024)	(1,878)
Changes in assets and liabilities:
Restricted cash	1,185	(83)
Accounts receivable	(2,200)	5,040
Straight-line rent receivables, net	(3,850)	(4,656)
Deferred leasing costs	(6,599)	(8,869)
Other assets	(1,767)	(2,140)
Accounts payable and other liabilities	8,137	17,734
Tenants’ security and escrow deposits and prepaid rent	4,550	(5,559)
Net cash provided by operating activities	200,562	196,054
Cash flows from investing activities:
Acquisition of operating real estate	(26,676)	(58,015)
Development of real estate, including acquisition of land	(162,419)	(117,550)
Proceeds from sale of real estate investments	136,997	315,235
Payments for (Proceeds from) Loans Receivable	(6,015)	579
Investments in real estate partnerships	(10,844)	(53,587)
Distributions received from investments in real estate partnerships	31,457	29,463
Dividends on trading securities held in trust	95	130
Acquisition of securities	(17,795)	(13,635)
Proceeds from sale of securities	12,732	13,900
Net cash (used in) provided by investing activities	(30,438)	115,362
Proceeds from Issuance of Common Stock	99,753	21,677
Cash flows from financing activities:
Net proceeds from issuance of preferred stock	0	313,505
Proceeds from sale of treasury stock	34	339
Acquisition of treasury stock	0	(4)
Redemption of preferred stock and partnership units	0	(323,125)
Payments to Noncontrolling Interests	3,288	(1,484)
Distributions	(245)	(246)
Payments of Preferred Dividends, Noncontrolling Interest	0	(404)
Dividends, Common Stock, Cash	126,604	124,140
Dividends paid to common stockholders	(125,528)	(123,155)
Dividends paid to preferred stockholders	(15,797)	(13,373)
Repayment of debt	0	(192,377)
Proceeds from Lines of Credit	82,000	535,000
Repayments of Lines of Credit	(152,000)	(510,000)
Proceeds from notes payable	8,250	0
Repayments of Notes Payable	(16,439)	0
Scheduled principal payments	(6,352)	(6,484)
Payment of loan costs	(159)	(4,305)
Net cash used in financing activities	(129,771)	(301,468)
Net increase in cash and cash equivalents	40,353	9,948
Cash and cash equivalents at beginning of the period	22,349	11,402
Cash and cash equivalents at end of the period	62,702	21,350
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $4,174 and $2,477 in 2013 and 2012, respectively)	72,607	80,742
Supplemental disclosure of non-cash transactions:
Preferred unit and stock distribution declared and not paid	0	4,615
Stock Issued During Period, Value, Conversion of Units	302	0
Real estate received through distribution in kind	7,576	0
Mortgage loans assumed for the acquisition of real estate	0	0
Real Estate Owned, Transfer from Real Estate Owned	0	47,500
Noncash or Part Noncash Acquisition, Other Assets Acquired	7,646	0
Real estate acquired through elimination of note receivable	0	12,585
Change in fair value of derivative instruments	22,249	(67)
Stock-based compensation capitalized	1,567	1,453
Contributions from limited partners in consolidated partnerships, net	0	986
Common stock issued for dividend reinvestment in trust	489	439
Contribution of stock awards into trust	1,522	821
Distribution of stock held in trust	201	1,191
Partnership Interest [Member]
Cash flows from operating activities:
Net income	99,268	57,903
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	98,620	96,217
Amortization of deferred loan cost and debt premium	9,265	9,619
Accretion of above and below market lease intangibles, net	(1,646)	(667)
Stock-based compensation, net of capitalization	9,227	7,332
Equity in income of investments in real estate partnerships	(25,150)	(19,173)
Net gain on sale of properties	(29,235)	(10,646)
Provision for impairment	(6,000)	(24,655)
Gains (Losses) on Extinguishment of Debt	0	852
Distribution of earnings from operations of investments in real estate partnerships	(34,772)	(28,550)
Loss on derivative instruments	(14)	(17)
Deferred compensation expense	2,023	1,840
Realized and unrealized gains on trading securities held in trust	(2,024)	(1,878)
Changes in assets and liabilities:
Restricted cash	1,185	(83)
Accounts receivable	(2,200)	5,040
Straight-line rent receivables, net	(3,850)	(4,656)
Deferred leasing costs	(6,599)	(8,869)
Other assets	(1,767)	(2,140)
Accounts payable and other liabilities	8,137	17,734
Tenants’ security and escrow deposits and prepaid rent	4,550	(5,559)
Net cash provided by operating activities	200,562	196,054
Cash flows from investing activities:
Acquisition of operating real estate	(26,676)	(58,015)
Development of real estate, including acquisition of land	(162,419)	(117,550)
Proceeds from sale of real estate investments	136,997	315,235
Payments for (Proceeds from) Loans Receivable	(6,015)	579
Investments in real estate partnerships	(10,844)	(53,587)
Distributions received from investments in real estate partnerships	31,457	29,463
Dividends on trading securities held in trust	95	130
Acquisition of securities	(17,795)	(13,635)
Proceeds from sale of securities	12,732	13,900
Net cash (used in) provided by investing activities	(30,438)	115,362
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	99,753	21,677
Net proceeds from issuance of preferred stock	0	313,505
Proceeds from sale of treasury stock	34	339
Acquisition of treasury stock	0	(4)
Redemption of preferred stock and partnership units	0	(323,125)
Payments to Noncontrolling Interests	3,288	(1,484)
Dividends paid to common stockholders	(125,773)	(123,401)
Dividends paid to preferred stockholders	(15,797)	(13,777)
Repayment of debt	0	(192,377)
Proceeds from Lines of Credit	82,000	535,000
Repayments of Lines of Credit	(152,000)	(510,000)
Proceeds from notes payable	8,250	0
Repayments of Notes Payable	(16,439)	0
Scheduled principal payments	(6,352)	(6,484)
Payment of loan costs	(159)	(4,305)
Net cash used in financing activities	(129,771)	(301,468)
Net increase in cash and cash equivalents	40,353	9,948
Cash and cash equivalents at beginning of the period	22,349	11,402
Cash and cash equivalents at end of the period	62,702	21,350
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $4,174 and $2,477 in 2013 and 2012, respectively)	72,607	80,742
Supplemental disclosure of non-cash transactions:
Preferred unit and stock distribution declared and not paid	0	4,615
Stock Issued During Period, Value, Conversion of Units	302	0
Real estate received through distribution in kind	7,576	0
Mortgage loans assumed for the acquisition of real estate	0	0
Real Estate Owned, Transfer from Real Estate Owned	0	47,500
Noncash or Part Noncash Acquisition, Other Assets Acquired	7,646	0
Real estate acquired through elimination of note receivable	0	12,585
Change in fair value of derivative instruments	22,249	(67)
Common stock issued for dividend reinvestment plan	831	740
Stock-based compensation capitalized	1,567	1,453
Contributions from limited partners in consolidated partnerships, net	0	986
Common stock issued for dividend reinvestment in trust	489	439
Contribution of stock awards into trust	1,522	821
Distribution of stock held in trust	201	1,191
Grand Ridge Plaza [Member] | Parent Company [Member]
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed for the acquisition of real estate		12,810
Grand Ridge Plaza [Member] | Partnership Interest [Member]
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed for the acquisition of real estate		12,810
Hilltop Village [Member] | Parent Company [Member]
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed for the acquisition of real estate	7,500
Hilltop Village [Member] | Partnership Interest [Member]
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed for the acquisition of real estate	7,500
Total Noncontrolling Interests [Member] | Parent Company [Member]
Cash flows from operating activities:
Net income	1,055	123
Cash flows from financing activities:
Dividends, Common Stock, Cash		246
Total Noncontrolling Interests [Member] | Parent Company [Member] | Noncontrolling Interest Exchangeable Operating Partnership Units [Member]
Cash flows from financing activities:
Dividends, Common Stock, Cash	(245)
Noncontrolling Interest Exchangeable Operating Partnership Units [Member] | Parent Company [Member]
Cash flows from operating activities:
Net income	183	116
Cash flows from financing activities:
Dividends, Common Stock, Cash	245
Noncontrolling Interest Exchangeable Operating Partnership Units [Member] | Parent Company [Member] | Noncontrolling Interest Exchangeable Operating Partnership Units [Member]
Cash flows from financing activities:
Dividends, Common Stock, Cash		(246)
Common Stock [Member] | Parent Company [Member]
Supplemental disclosure of non-cash transactions:
Stock Issued During Period, Value, Conversion of Units	0
Common stock issued for dividend reinvestment plan	831	740
Common Stock [Member] | Total Noncontrolling Interests [Member] | Parent Company [Member]
Supplemental disclosure of non-cash transactions:
Stock Issued During Period, Value, Conversion of Units	(302)
Common stock issued for dividend reinvestment plan	0	0
Common Stock [Member] | Noncontrolling Interest Exchangeable Operating Partnership Units [Member] | Parent Company [Member]
Supplemental disclosure of non-cash transactions:
Stock Issued During Period, Value, Conversion of Units	(302)
Common stock issued for dividend reinvestment plan	$ 0	$ 0