Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Document Fiscal Year Focus	2015
Cash flows from investing activities:
Payments for Deposits on Real Estate Acquisitions	$ (2,300)
Cash flows from financing activities:
Net proceeds from common stock issuance	1,173	$ 49,995
Parent Company [Member]
Proceeds from Issuance of Unsecured Debt	248,160	248,705
Cash flows from operating activities:
Net income	129,004	109,659
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	109,249	110,355
Amortization of deferred loan cost and debt premium	7,404	8,095
Amortization and (accretion) of above and below market lease intangibles, net	(1,250)	(2,315)
Stock-based compensation, net of capitalization	8,379	6,885
Equity in income of investments in real estate partnerships	(17,991)	(22,353)
Gain on sale of real estate	(34,215)	(29,598)
Provision for impairment	0	(225)
Early extinguishment of debt	61	0
Distribution of earnings from operations of investments in real estate partnerships	(34,527)	(30,008)
Loss on settlement of derivative instruments	7,267	(4,648)
Gain on derivative instruments	0	(13)
Deferred compensation expense	(610)	610
Realized and unrealized loss (gain) on investments	189	(612)
Changes in assets and liabilities:
Restricted cash	1,534	497
Accounts receivable	(4,408)	(2,801)
Straight-line rent receivables, net	(6,274)	(4,724)
Deferred leasing costs	(8,268)	(6,416)
Other assets	(2,257)	131
Accounts payable and other liabilities	10,230	15,018
Tenants’ security, escrow deposits and prepaid rent	(1,152)	511
Net cash provided by operating activities	216,763	217,810
Cash flows from investing activities:
Acquisition of operating real estate	(42,983)	(98,018)
Payments for Deposits on Real Estate Acquisitions	(2,250)	0
Real estate development and capital improvements	(150,967)	(160,552)
Proceeds from sale of real estate investments	93,727	62,788
Collection of notes receivable	1,000	0
Investments in real estate partnerships	(18,644)	(6,012)
Distributions received from investments in real estate partnerships	15,014	29,916
Dividends on investments	128	100
Acquisition of securities	(25,675)	(19,866)
Proceeds from sale of securities	22,296	5,344
Net cash used in investing activities	(108,354)	(186,300)
Cash flows from financing activities:
Net proceeds from common stock issuance	946	49,300
Proceeds from sale of treasury stock	51	0
Redemption of preferred stock and partnership units	0	(300)
Distributions to limited partners in consolidated partnerships, net	(2,352)	(4,619)
Distributions to exchangeable operating partnership unit holders	(223)	(228)
Dividends paid to common stockholders	(136,008)	(129,044)
Dividends paid to preferred stockholders	(15,797)	(15,797)
Proceeds from unsecured credit facilities	445,000	255,000
Repayment of unsecured credit facilities	(305,000)	(255,000)
Proceeds from notes payable	3,325	12,025
Repayments of Notes Payable	76,027	13,487
Scheduled principal payments	(4,384)	(5,068)
Payment of loan costs	(5,996)	(2,973)
Net cash used in financing activities	(198,305)	(11,486)
Repayments of Unsecured Debt	350,000	150,000
Net (decrease) increase in cash and cash equivalents	(89,896)	20,024
Cash and cash equivalents at beginning of the period	113,776	80,684
Cash and cash equivalents at end of the period	23,880	100,708
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $5,403 and $5,158 in 2015 and 2014, respectively)	71,734	72,573
Income Taxes Paid	871	94
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed for the acquisition of real estate	42,799	78,049
Change in fair value of derivative instruments	(10,845)	(28,144)
Common stock issued for dividend reinvestment plan	966	895
Stock-based compensation capitalized	2,196	2,026
Contributions from limited partners in consolidated partnerships, net	13	116
Non-controlling interest recorded, fair value	0	15,385
Common stock issued for dividend reinvestment in trust	631	581
Contribution of stock awards into trust	1,633	1,865
Distribution of stock held in trust	1,898	4
Unrealized Gain (Loss) on Securities	(73)	4,809
Partnership Interest [Member]
Proceeds from Issuance of Unsecured Debt	248,160	248,705
Cash flows from operating activities:
Net income	129,004	109,659
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	109,249	110,355
Amortization of deferred loan cost and debt premium	7,404	8,095
Amortization and (accretion) of above and below market lease intangibles, net	(1,250)	(2,315)
Stock-based compensation, net of capitalization	8,379	6,885
Equity in income of investments in real estate partnerships	(17,991)	(22,353)
Gain on sale of real estate	(34,215)	(29,598)
Provision for impairment	0	(225)
Early extinguishment of debt	61	0
Distribution of earnings from operations of investments in real estate partnerships	(34,527)	(30,008)
Loss on settlement of derivative instruments	7,267	(4,648)
Gain on derivative instruments	0	(13)
Deferred compensation expense	(610)	610
Realized and unrealized loss (gain) on investments	189	(612)
Changes in assets and liabilities:
Restricted cash	1,534	497
Accounts receivable	(4,408)	(2,801)
Straight-line rent receivables, net	(6,274)	(4,724)
Deferred leasing costs	(8,268)	(6,416)
Other assets	(2,257)	131
Accounts payable and other liabilities	10,230	15,018
Tenants’ security, escrow deposits and prepaid rent	(1,152)	511
Net cash provided by operating activities	216,763	217,810
Cash flows from investing activities:
Acquisition of operating real estate	(42,983)	(98,018)
Payments for Deposits on Real Estate Acquisitions	(2,250)	0
Real estate development and capital improvements	(150,967)	(160,552)
Proceeds from sale of real estate investments	93,727	62,788
Collection of notes receivable	1,000	0
Investments in real estate partnerships	(18,644)	(6,012)
Distributions received from investments in real estate partnerships	15,014	29,916
Dividends on investments	128	100
Acquisition of securities	(25,675)	(19,866)
Proceeds from sale of securities	22,296	5,344
Net cash used in investing activities	(108,354)	(186,300)
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	946	49,300
Proceeds from sale of treasury stock	51	0
Redemption of preferred stock and partnership units	0	(300)
Distributions to limited partners in consolidated partnerships, net	(2,352)	(4,619)
Dividends paid to common stockholders	(136,231)	(129,272)
Dividends paid to preferred stockholders	(15,797)	(15,797)
Proceeds from unsecured credit facilities	445,000	255,000
Repayment of unsecured credit facilities	(305,000)	(255,000)
Proceeds from notes payable	3,325	12,025
Repayments of Notes Payable	76,027	13,487
Scheduled principal payments	(4,384)	(5,068)
Payment of loan costs	(5,996)	(2,973)
Net cash used in financing activities	(198,305)	(11,486)
Repayments of Unsecured Debt	350,000	150,000
Net (decrease) increase in cash and cash equivalents	(89,896)	20,024
Cash and cash equivalents at beginning of the period	113,776	80,684
Cash and cash equivalents at end of the period	23,880	100,708
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $5,403 and $5,158 in 2015 and 2014, respectively)	71,734	72,573
Income Taxes Paid	871	94
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed for the acquisition of real estate	42,799	78,049
Change in fair value of derivative instruments	(10,845)	(28,144)
Common stock issued for dividend reinvestment plan	966	895
Stock-based compensation capitalized	2,196	2,026
Contributions from limited partners in consolidated partnerships, net	13	116
Non-controlling interest recorded, fair value	0	15,385
Common stock issued for dividend reinvestment in trust	631	581
Contribution of stock awards into trust	1,633	1,865
Distribution of stock held in trust	1,898	4
Unrealized Gain (Loss) on Securities	$ (73)	$ 4,809