Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation, net of capitalization	$ 2,272	$ 3,024
Net gain on sale of properties	(715)
Cash flows from investing activities:
Proceeds from sale of real estate investments	4,472
Cash flows from financing activities:
Net proceeds from common stock issuance		52,398
Parent Company [Member]
Cash flows from operating activities:
Net income	25,056	21,134
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	37,905	32,764
Amortization of deferred loan cost and debt premium	2,889	3,087
Accretion of above and below market lease intangibles, net	(861)	(510)
Stock-based compensation, net of capitalization	2,272	3,024
Equity in income of investments in real estate partnerships	(7,808)	(5,876)
Net gain on sale of properties	(715)	0
Provision for impairment	(225)	0
Distribution of earnings from operations of investments in real estate partnerships	(8,681)	(13,859)
Loss on derivative instruments	(5)	(5)
Deferred compensation expense	200	1,079
Realized and unrealized gains on trading securities held in trust	(201)	(1,079)
Changes in assets and liabilities:
Restricted cash	328	382
Accounts receivable	(6,740)	(2,689)
Straight-line rent receivables, net	(1,594)	(1,413)
Deferred leasing costs	(1,961)	(1,983)
Other assets	(1,952)	(1,383)
Accounts payable and other liabilities	(4,858)	(15,540)
Tenants’ security and escrow deposits and prepaid rent	1,403	(3,569)
Net cash provided by operating activities	52,264	41,282
Cash flows from investing activities:
Acquisition of operating real estate	(78,943)	0
Development of real estate, including acquisition of land	(46,648)	(32,348)
Proceeds from sale of real estate investments	4,472	96
Collection of notes receivable	0	4,024
Investments in real estate partnerships	(1,771)	(4,060)
Distributions received from investments in real estate partnerships	5,931	7,187
Dividends on trading securities held in trust	27	33
Acquisition of securities	(1,797)	(7,039)
Proceeds from sale of securities	1,676	2,019
Net cash used in investing activities	(117,053)	(30,088)
Cash flows from financing activities:
Net proceeds from common stock issuance	0	51,608
Proceeds from sale of treasury stock	0	34
Redemption of preferred stock and partnership units	(300)	0
Distributions to limited partners in consolidated partnerships, net	(426)	(2,483)
Distributions to exchangeable operating partnership unit holders	(78)	(90)
Dividends paid to common stockholders	(42,947)	(41,290)
Dividends paid to preferred stockholders	(5,266)	0
Proceeds from unsecured credit facilities	70,000	37,000
Repayment of unsecured credit facilities	0	(62,000)
Proceeds from notes payable	0	8,250
Scheduled principal payments	(1,719)	(2,059)
Payment of loan costs	0	(111)
Net cash provided by (used in) financing activities	19,264	(11,141)
Net (decrease) increase in cash and cash equivalents	(45,525)	53
Cash and cash equivalents at beginning of the period	80,684	22,349
Cash and cash equivalents at end of the period	35,159	22,402
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $1,641 and $1,062 in 2014 and 2013, respectively)	18,338	19,017
Supplemental disclosure of non-cash transactions:
Preferred unit and stock distribution declared and not paid	0	5,266
Real estate received through distribution in kind	0	7,700
Mortgage loans assumed through distribution in kind	0	7,500
Mortgage loans assumed for the acquisition of real estate, net of premiums	78,049	0
Change in fair value of derivative instruments	(13,648)	3,385
Common stock issued for dividend reinvestment plan	313	288
Stock-based compensation capitalized	696	391
Contributions from limited partners in consolidated partnerships, net	58	0
Common stock issued for dividend reinvestment in trust	189	153
Contribution of stock awards into trust	1,440	1,068
Distribution of stock held in trust	4	201
Partnership Interest [Member]
Cash flows from operating activities:
Net income	25,056	21,134
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	37,905	32,764
Amortization of deferred loan cost and debt premium	2,889	3,087
Accretion of above and below market lease intangibles, net	(861)	(510)
Stock-based compensation, net of capitalization	2,272	3,024
Equity in income of investments in real estate partnerships	(7,808)	(5,876)
Net gain on sale of properties	(715)	0
Provision for impairment	(225)	0
Distribution of earnings from operations of investments in real estate partnerships	(8,681)	(13,859)
Loss on derivative instruments	(5)	(5)
Deferred compensation expense	200	1,079
Realized and unrealized gains on trading securities held in trust	(201)	(1,079)
Changes in assets and liabilities:
Restricted cash	328	382
Accounts receivable	(6,740)	(2,689)
Straight-line rent receivables, net	(1,594)	(1,413)
Deferred leasing costs	(1,961)	(1,983)
Other assets	(1,952)	(1,383)
Accounts payable and other liabilities	(4,858)	(15,540)
Tenants’ security and escrow deposits and prepaid rent	1,403	(3,569)
Net cash provided by operating activities	52,264	41,282
Cash flows from investing activities:
Acquisition of operating real estate	(78,943)	0
Development of real estate, including acquisition of land	(46,648)	(32,348)
Proceeds from sale of real estate investments	4,472	96
Collection of notes receivable	0	4,024
Investments in real estate partnerships	(1,771)	(4,060)
Distributions received from investments in real estate partnerships	5,931	7,187
Dividends on trading securities held in trust	27	33
Acquisition of securities	(1,797)	(7,039)
Proceeds from sale of securities	1,676	2,019
Net cash used in investing activities	(117,053)	(30,088)
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	0	51,608
Proceeds from sale of treasury stock	0	34
Redemption of preferred stock and partnership units	(300)	0
Distributions to limited partners in consolidated partnerships, net	(426)	(2,483)
Dividends paid to common stockholders	(43,025)	(41,380)
Dividends paid to preferred stockholders	(5,266)	0
Proceeds from unsecured credit facilities	70,000	37,000
Repayment of unsecured credit facilities	0	(62,000)
Proceeds from notes payable	0	8,250
Scheduled principal payments	(1,719)	(2,059)
Payment of loan costs	0	(111)
Net cash provided by (used in) financing activities	19,264	(11,141)
Net (decrease) increase in cash and cash equivalents	(45,525)	53
Cash and cash equivalents at beginning of the period	80,684	22,349
Cash and cash equivalents at end of the period	35,159	22,402
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $1,641 and $1,062 in 2014 and 2013, respectively)	18,338	19,017
Supplemental disclosure of non-cash transactions:
Preferred unit and stock distribution declared and not paid	0	5,266
Real estate received through distribution in kind	0	7,700
Mortgage loans assumed through distribution in kind	0	7,500
Mortgage loans assumed for the acquisition of real estate, net of premiums	78,049	0
Change in fair value of derivative instruments	(13,648)	3,385
Common stock issued for dividend reinvestment plan	313	288
Stock-based compensation capitalized	696	391
Contributions from limited partners in consolidated partnerships, net	58	0
Non-controlling interest recorded, fair value		0
Common stock issued for dividend reinvestment in trust	189	153
Contribution of stock awards into trust	1,440	1,068
Distribution of stock held in trust	$ 4	$ 201