Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from investing activities:
Proceeds from sale of real estate investments	$ 38,705	$ 26,382
Parent Company [Member]
Cash flows from operating activities:
Net income	94,221	69,271
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	79,015	72,218
Amortization of deferred loan cost and debt premium	4,831	5,058
(Accretion) and amortization of above and below market lease intangibles, net	(1,176)	(936)
Share-based Compensation	5,189	5,620
Stock-based compensation, net of capitalization	1,723	1,493
Equity in income of investments in real estate partnerships	(23,971)	(12,324)
Gain on sale of real estate	(13,417)	(6,460)
Provision for impairment	(1,666)	0
Early extinguishment of debt	0	61
Distribution of earnings from operations of investments in real estate partnerships	(26,159)	(22,719)
Deferred compensation expense	429	581
Realized and unrealized loss (gain) on investments	(446)	(1,000)
Increase (Decrease) in Restricted Cash for Operating Activities	31	(1,587)
Changes in assets and liabilities:
Accounts receivable, net	(6,841)	(5,895)
Straight-line rent receivables, net	(3,071)	(3,552)
Deferred leasing costs	(5,386)	(5,470)
Other assets	(1,718)	(3,209)
Accounts payable and other liabilities	(9,447)	(12,004)
Tenants’ security, escrow deposits and prepaid rent	(2,693)	1,270
Net cash provided by operating activities	143,313	127,413
Cash flows from investing activities:
Acquisition of operating real estate	(297,448)	0
Payments for Deposits on Real Estate Acquisitions	(1,500)	(4,500)
Real estate development and capital improvements	(75,320)	(109,118)
Proceeds from sale of real estate investments	36,751	26,567
Investments in real estate partnerships	(3,823)	(1,344)
Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital	25,746	15,014
Dividends on investment securities	137	87
Acquisition of securities	(46,306)	(20,581)
Proceeds from sale of securities	45,739	17,169
Net cash used in investing activities	(316,024)	(76,706)
Cash flows from financing activities:
Net proceeds from common stock issuance	149,788	955
Proceeds from sale of treasury stock	904	0
Distributions to limited partners in consolidated partnerships, net	(2,214)	(1,722)
Distributions to exchangeable operating partnership unit holders	(154)	(151)
Dividends paid to common stockholders	(97,061)	(90,625)
Dividends paid to preferred stockholders	(10,531)	(10,531)
Proceeds from unsecured credit facilities	295,000	85,000
Repayment of unsecured credit facilities	(150,000)	(40,000)
Proceeds from notes payable	20,000	2,399
Repayments of Notes Payable	(41,584)	(76,027)
Scheduled principal payments	(3,062)	(2,921)
Payment of loan costs	(292)	(3,746)
Net cash provided by (used in) financing activities	160,794	(137,369)
Net decrease in cash and cash equivalents	(11,917)	(86,662)
Cash and cash equivalents at beginning of the period	36,856	113,776
Cash and cash equivalents at end of the period	24,939	27,114
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $1,766 and $4,015 in 2016 and 2015, respectively)	44,153	53,458
Income Taxes Paid	0	697
Supplemental disclosure of non-cash transactions:
Change in fair value of derivative instruments	(26,630)	4,494
Common stock issued for dividend reinvestment plan	547	683
Contributions from limited partners in consolidated partnerships, net	8,420	13
Common stock issued for dividend reinvestment in trust	384	432
Contribution of stock awards into trust	1,488	1,475
Distribution of stock held in trust	4,060	1,898
Unrealized Gain (Loss) on Securities	37	(30)
Partnership Interest [Member]
Cash flows from operating activities:
Net income	94,221	69,271
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	79,015	72,218
Amortization of deferred loan cost and debt premium	4,831	5,058
(Accretion) and amortization of above and below market lease intangibles, net	(1,176)	(936)
Share-based Compensation	5,189	5,620
Stock-based compensation, net of capitalization	1,723	1,493
Equity in income of investments in real estate partnerships	(23,971)	(12,324)
Gain on sale of real estate	(13,417)	(6,460)
Provision for impairment	(1,666)	0
Early extinguishment of debt	0	61
Distribution of earnings from operations of investments in real estate partnerships	(26,159)	(22,719)
Deferred compensation expense	429	581
Realized and unrealized loss (gain) on investments	(446)	(1,000)
Increase (Decrease) in Restricted Cash for Operating Activities	31	(1,587)
Changes in assets and liabilities:
Accounts receivable, net	(6,841)	(5,895)
Straight-line rent receivables, net	(3,071)	(3,552)
Deferred leasing costs	(5,386)	(5,470)
Other assets	(1,718)	(3,209)
Accounts payable and other liabilities	(9,447)	(12,004)
Tenants’ security, escrow deposits and prepaid rent	(2,693)	1,270
Net cash provided by operating activities	143,313	127,413
Cash flows from investing activities:
Acquisition of operating real estate	(297,448)	0
Payments for Deposits on Real Estate Acquisitions	(1,500)	(4,500)
Real estate development and capital improvements	(75,320)	(109,118)
Proceeds from sale of real estate investments	36,751	26,567
Investments in real estate partnerships	(3,823)	(1,344)
Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital	25,746	15,014
Dividends on investment securities	137	87
Acquisition of securities	(46,306)	(20,581)
Proceeds from sale of securities	45,739	17,169
Net cash used in investing activities	(316,024)	(76,706)
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	149,788	955
Proceeds from sale of treasury stock	904	0
Distributions to limited partners in consolidated partnerships, net	(2,214)	(1,722)
Dividends paid to common stockholders	(97,215)	(90,776)
Dividends paid to preferred stockholders	(10,531)	(10,531)
Proceeds from unsecured credit facilities	295,000	85,000
Repayment of unsecured credit facilities	(150,000)	(40,000)
Proceeds from notes payable	20,000	2,399
Repayments of Notes Payable	(41,584)	(76,027)
Scheduled principal payments	(3,062)	(2,921)
Payment of loan costs	(292)	(3,746)
Net cash provided by (used in) financing activities	160,794	(137,369)
Net decrease in cash and cash equivalents	(11,917)	(86,662)
Cash and cash equivalents at beginning of the period	36,856	113,776
Cash and cash equivalents at end of the period	24,939	27,114
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $1,766 and $4,015 in 2016 and 2015, respectively)	44,153	53,458
Income Taxes Paid	0	697
Supplemental disclosure of non-cash transactions:
Change in fair value of derivative instruments	(26,630)	4,494
Common stock issued for dividend reinvestment plan	547	683
Contributions from limited partners in consolidated partnerships, net	8,420	13
Non-controlling interest recorded, fair value	0	0
Common stock issued for dividend reinvestment in trust	384	432
Contribution of stock awards into trust	1,488	1,475
Distribution of stock held in trust	4,060	1,898
Unrealized Gain (Loss) on Securities	$ 37	$ (30)