Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 105,334	$ 129,004
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for impairment	(1,666)	0
Cash flows from investing activities:
Proceeds from sale of real estate investments	85,885	93,727
Parent Company [Member]
Proceeds from Issuance of Unsecured Debt	0	248,160
Cash flows from operating activities:
Net income	105,334	129,004
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	119,721	109,249
Amortization of deferred loan cost and debt premium	7,242	7,404
(Accretion) and amortization of above and below market lease intangibles, net	(2,296)	(1,250)
Share-based Compensation	7,554	8,379
Stock-based compensation, net of capitalization	2,561	2,196
Equity in income of investments in real estate partnerships	(46,618)	(17,991)
Gain on sale of real estate, net of tax	(22,997)	(34,215)
Provision for impairment	(1,666)	0
Early extinguishment of debt	(13,943)	61
(Payments for) Proceeds from Settlement of Derivative Instrument	0	(7,267)
Distribution of earnings from operations of investments in real estate partnerships	(39,765)	(34,527)
Deferred compensation expense	1,249	(610)
Realized and unrealized loss (gain) on investments	(1,268)	189
Increase (Decrease) in Restricted Cash for Operating Activities	84	(1,534)
Changes in assets and liabilities:
Accounts receivable, net	(4,269)	(4,408)
Straight-line rent receivables, net	(4,894)	(6,274)
Deferred leasing costs	(7,841)	(8,268)
Other assets	(59)	(2,257)
Accounts payable and other liabilities	12,607	10,230
Tenants’ security, escrow deposits and prepaid rent	(1,406)	(1,152)
Net cash provided by operating activities	217,349	216,763
Cash flows from investing activities:
Acquisition of operating real estate	(333,220)	(42,983)
Payments for Deposits on Real Estate Acquisitions	1,250	(2,250)
Real estate development and capital improvements	(146,773)	(150,967)
Proceeds from sale of real estate investments	83,675	93,727
Payments for (Proceeds from) Loans Receivable	0	(1,000)
Investments in real estate partnerships	(13,127)	(18,644)
Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital	52,536	15,014
Dividends on investment securities	189	128
Acquisition of securities	(53,290)	(25,675)
Proceeds from sale of securities	54,176	22,296
Net cash used in investing activities	(354,584)	(108,354)
Cash flows from financing activities:
Net proceeds from common stock issuance	549,545	946
Proceeds from sale of treasury stock	957	51
Distributions to limited partners in consolidated partnerships, net	(3,126)	(2,352)
Distributions to exchangeable operating partnership unit holders	(229)	(223)
Dividends paid to common stockholders	(149,049)	(136,008)
Dividends paid to preferred stockholders	(15,797)	(15,797)
Proceeds from unsecured credit facilities	395,000	445,000
Repayment of unsecured credit facilities	(295,000)	(305,000)
Proceeds from notes payable	20,223	3,325
Repayments of Notes Payable	(41,584)	(76,027)
Scheduled principal payments	(4,462)	(4,384)
Payment of loan costs	(1,954)	(5,996)
Payments of Debt Extinguishment Costs	(13,214)	0
Net cash provided by (used in) financing activities	141,281	(198,305)
Repayments of Unsecured Debt	300,000	350,000
Payments for Repurchase of Common Stock	29	0
Cash and cash equivalents at beginning of the period	36,856	113,776
Cash and cash equivalents at end of the period	40,902	23,880
Net increase (decrease) in cash and cash equivalents	4,046	(89,896)
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $2,622 and $5,403 in 2016 and 2015, respectively)	54,904	71,734
Income Taxes Paid	0	871
Supplemental disclosure of non-cash transactions:
Noncash or Part Noncash Acquisition, Debt Assumed	0	42,799
Change in fair value of derivative instruments	(25,338)	(10,845)
Common stock issued for dividend reinvestment plan	804	966
Contributions from limited partners in consolidated partnerships, net	8,674	13
Common stock issued for dividend reinvestment in trust	556	631
Contribution of stock awards into trust	1,513	1,633
Distribution of stock held in trust	4,096	1,898
Unrealized Gain (Loss) on Securities	90	(73)
Deconsolidation of previously consolidated partnership [Abstract]
Deconsolidation of consolidated partnership, Real estate, net	14,075	0
Deconsolidation of consolidated partnership, Return of capital	(3,355)	0
Deconsolidation of consolidated partnership, Mortgage Notes Payable	(9,415)	0
Deconsolidation of consolidated partnership, Other assets and liabilities	640	0
Deconsolidation of consolidated partnership, Noncontrolling Interest	(2,099)	0
Partnership Interest [Member]
Proceeds from Issuance of Unsecured Debt	0	248,160
Cash flows from operating activities:
Net income	105,334	129,004
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	119,721	109,249
Amortization of deferred loan cost and debt premium	7,242	7,404
(Accretion) and amortization of above and below market lease intangibles, net	(2,296)	(1,250)
Share-based Compensation	7,554	8,379
Stock-based compensation, net of capitalization	2,561	2,196
Equity in income of investments in real estate partnerships	(46,618)	(17,991)
Gain on sale of real estate, net of tax	(22,997)	(34,215)
Provision for impairment	(1,666)	0
Early extinguishment of debt	(13,943)	61
(Payments for) Proceeds from Settlement of Derivative Instrument	0	(7,267)
Distribution of earnings from operations of investments in real estate partnerships	(39,765)	(34,527)
Deferred compensation expense	1,249	(610)
Realized and unrealized loss (gain) on investments	(1,268)	189
Increase (Decrease) in Restricted Cash for Operating Activities	84	(1,534)
Changes in assets and liabilities:
Accounts receivable, net	(4,269)	(4,408)
Straight-line rent receivables, net	(4,894)	(6,274)
Deferred leasing costs	(7,841)	(8,268)
Other assets	(59)	(2,257)
Accounts payable and other liabilities	12,607	10,230
Tenants’ security, escrow deposits and prepaid rent	(1,406)	(1,152)
Net cash provided by operating activities	217,349	216,763
Cash flows from investing activities:
Acquisition of operating real estate	(333,220)	(42,983)
Payments for Deposits on Real Estate Acquisitions	1,250	(2,250)
Real estate development and capital improvements	(146,773)	(150,967)
Proceeds from sale of real estate investments	83,675	93,727
Payments for (Proceeds from) Loans Receivable	0	(1,000)
Investments in real estate partnerships	(13,127)	(18,644)
Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital	52,536	15,014
Dividends on investment securities	189	128
Acquisition of securities	(53,290)	(25,675)
Proceeds from sale of securities	54,176	22,296
Net cash used in investing activities	(354,584)	(108,354)
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	549,545	946
Proceeds from sale of treasury stock	957	51
Distributions to limited partners in consolidated partnerships, net	(3,126)	(2,352)
Dividends paid to common stockholders	(149,278)	(136,231)
Dividends paid to preferred stockholders	(15,797)	(15,797)
Proceeds from unsecured credit facilities	395,000	445,000
Repayment of unsecured credit facilities	(295,000)	(305,000)
Proceeds from notes payable	20,223	3,325
Repayments of Notes Payable	(41,584)	(76,027)
Scheduled principal payments	(4,462)	(4,384)
Payment of loan costs	(1,954)	(5,996)
Payments of Debt Extinguishment Costs	(13,214)	0
Net cash provided by (used in) financing activities	141,281	(198,305)
Repayments of Unsecured Debt	300,000	350,000
Payments for Repurchase of Common Stock	29	0
Cash and cash equivalents at beginning of the period	36,856	113,776
Cash and cash equivalents at end of the period	40,902	23,880
Net increase (decrease) in cash and cash equivalents	4,046	(89,896)
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $2,622 and $5,403 in 2016 and 2015, respectively)	54,904	71,734
Income Taxes Paid	0	871
Supplemental disclosure of non-cash transactions:
Change in fair value of derivative instruments	(25,338)	(10,845)
Common stock issued for dividend reinvestment plan	804	966
Contributions from limited partners in consolidated partnerships, net	8,674	13
Non-controlling interest recorded, fair value	0	0
Common stock issued for dividend reinvestment in trust	556	631
Contribution of stock awards into trust	1,513	1,633
Distribution of stock held in trust	4,096	1,898
Unrealized Gain (Loss) on Securities	90	(73)
Deconsolidation of previously consolidated partnership [Abstract]
Deconsolidation of consolidated partnership, Real estate, net	14,075	0
Deconsolidation of consolidated partnership, Return of capital	(3,355)	0
Deconsolidation of consolidated partnership, Mortgage Notes Payable	(9,415)	0
Deconsolidation of consolidated partnership, Other assets and liabilities	640	0
Deconsolidation of consolidated partnership, Noncontrolling Interest	$ (2,099)	$ 0