Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from investing activities:
Payments for Deposits on Real Estate Acquisitions	$ (1,300)
Proceeds from sale of real estate investments	34,321	$ 3,414
Cash flows from financing activities:
Net proceeds from common stock issuance	12,584	1,173
Parent Company [Member]
Cash flows from operating activities:
Net income	53,577	30,992
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	38,716	35,992
Amortization of deferred loan cost and debt premium	2,353	2,447
Amortization and (accretion) of above and below market lease intangibles, net	(351)	(521)
Share-based Compensation	2,621	2,900
Stock-based compensation, net of capitalization	814	701
Equity in income of investments in real estate partnerships	(12,920)	(5,567)
Gain on sale of real estate	(12,868)	(803)
Provision for impairment	(1,666)	0
Early extinguishment of debt	0	61
Distribution of earnings from operations of investments in real estate partnerships	(13,840)	(12,301)
Deferred compensation expense	(148)	631
Realized and unrealized loss (gain) on investments	155	(634)
Increase (Decrease) in Restricted Cash for Operating Activities	109	(1,415)
Changes in assets and liabilities:
Accounts receivable	(3,613)	(7,827)
Straight-line rent receivables, net	(1,848)	(1,877)
Deferred leasing costs	(2,903)	(1,816)
Other assets	(746)	(1,137)
Accounts payable and other liabilities	(7,286)	(13,101)
Tenants’ security, escrow deposits and prepaid rent	(1,301)	1,124
Net cash provided by operating activities	68,835	54,458
Cash flows from investing activities:
Acquisition of operating real estate	(16,483)	0
Payments for Deposits on Real Estate Acquisitions	0	(4,000)
Real estate development and capital improvements	(38,289)	(55,047)
Proceeds from sale of real estate investments	32,261	3,414
Investments in real estate partnerships	(2,438)	(1,344)
Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital	18,296	2,717
Dividends on investments	59	31
Acquisition of securities	(41,946)	(3,726)
Proceeds from sale of securities	41,207	2,868
Net cash used in investing activities	(7,333)	(55,087)
Cash flows from financing activities:
Net proceeds from common stock issuance	12,293	992
Proceeds from sale of treasury stock	904	0
Distributions to limited partners in consolidated partnerships, net	(1,707)	(1,050)
Distributions to exchangeable operating partnership unit holders	(77)	(76)
Dividends paid to common stockholders	(48,510)	(45,273)
Dividends paid to preferred stockholders	(5,266)	(5,266)
Proceeds from unsecured credit facilities	10,000	40,000
Repayment of unsecured credit facilities	(10,000)	(10,000)
Proceeds from notes payable	0	1,351
Repayments of Notes Payable	27,281	55,777
Scheduled principal payments	(1,572)	(1,481)
Payment of loan costs	(5)	(78)
Net cash used in financing activities	(71,221)	(76,658)
Net decrease in cash and cash equivalents	(9,719)	(77,287)
Cash and cash equivalents at beginning of the period	36,856	113,776
Cash and cash equivalents at end of the period	27,137	36,489
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $973 and $2,059 in 2016 and 2015, respectively)	7,611	17,964
Income Taxes Paid	0	697
Supplemental disclosure of non-cash transactions:
Change in fair value of derivative instruments	(16,785)	(13,882)
Common stock issued for dividend reinvestment plan	292	374
Contributions from limited partners in consolidated partnerships, net	8,362	13
Common stock issued for dividend reinvestment in trust	190	214
Contribution of stock awards into trust	958	1,042
Distribution of stock held in trust	1,807	0
Unrealized Gain (Loss) on Securities	(36)	0
Partnership Interest [Member]
Cash flows from operating activities:
Net income	53,577	30,992
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	38,716	35,992
Amortization of deferred loan cost and debt premium	2,353	2,447
Amortization and (accretion) of above and below market lease intangibles, net	(351)	(521)
Share-based Compensation	2,621	2,900
Stock-based compensation, net of capitalization	814	701
Equity in income of investments in real estate partnerships	(12,920)	(5,567)
Gain on sale of real estate	(12,868)	(803)
Provision for impairment	(1,666)	0
Early extinguishment of debt	0	61
Distribution of earnings from operations of investments in real estate partnerships	(13,840)	(12,301)
Deferred compensation expense	(148)	631
Realized and unrealized loss (gain) on investments	155	(634)
Increase (Decrease) in Restricted Cash for Operating Activities	109	(1,415)
Changes in assets and liabilities:
Accounts receivable	(3,613)	(7,827)
Straight-line rent receivables, net	(1,848)	(1,877)
Deferred leasing costs	(2,903)	(1,816)
Other assets	(746)	(1,137)
Accounts payable and other liabilities	(7,286)	(13,101)
Tenants’ security, escrow deposits and prepaid rent	(1,301)	1,124
Net cash provided by operating activities	68,835	54,458
Cash flows from investing activities:
Acquisition of operating real estate	(16,483)	0
Payments for Deposits on Real Estate Acquisitions	0	(4,000)
Real estate development and capital improvements	(38,289)	(55,047)
Proceeds from sale of real estate investments	32,261	3,414
Investments in real estate partnerships	(2,438)	(1,344)
Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital	18,296	2,717
Dividends on investments	59	31
Acquisition of securities	(41,946)	(3,726)
Proceeds from sale of securities	41,207	2,868
Net cash used in investing activities	(7,333)	(55,087)
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	12,293	992
Proceeds from sale of treasury stock	904	0
Distributions to limited partners in consolidated partnerships, net	(1,707)	(1,050)
Dividends paid to common stockholders	(48,587)	(45,349)
Dividends paid to preferred stockholders	(5,266)	(5,266)
Proceeds from unsecured credit facilities	10,000	40,000
Repayment of unsecured credit facilities	(10,000)	(10,000)
Proceeds from notes payable	0	1,351
Repayments of Notes Payable	27,281	55,777
Scheduled principal payments	(1,572)	(1,481)
Payment of loan costs	(5)	(78)
Net cash used in financing activities	(71,221)	(76,658)
Net decrease in cash and cash equivalents	(9,719)	(77,287)
Cash and cash equivalents at beginning of the period	36,856	113,776
Cash and cash equivalents at end of the period	27,137	36,489
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $973 and $2,059 in 2016 and 2015, respectively)	7,611	17,964
Income Taxes Paid	0	697
Supplemental disclosure of non-cash transactions:
Change in fair value of derivative instruments	(16,785)	(13,882)
Common stock issued for dividend reinvestment plan	292	374
Contributions from limited partners in consolidated partnerships, net	8,362	13
Non-controlling interest recorded, fair value	0	0
Common stock issued for dividend reinvestment in trust	190	214
Contribution of stock awards into trust	958	1,042
Distribution of stock held in trust	1,807	0
Unrealized Gain (Loss) on Securities	$ (36)	$ 0