Consolidated Balance Sheets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Document Fiscal Year Focus	2015
Real estate investments at cost (notes 2 and 3):
Investments in real estate partnerships (note 4)	$ 306,206	$ 333,167
Accounts receivable, net of allowance for doubtful accounts of $5,295 and $4,523 at December 31, 2015 and 2014, respectively	32,292	30,999
Acquired lease intangible assets, less accumulated amortization of $45,639 and $36,112 at December 31, 2015 and 2014, respectively (note 6)	105,380	52,365
Parent Company [Member]
Real estate investments at cost (notes 2 and 3):
Land	1,432,468	1,380,211
Buildings and improvements	2,896,396	2,790,137
Properties in development	217,036	239,538
Gross real estate investments at cost	4,545,900	4,409,886
Less: accumulated depreciation	1,043,787	933,708
Total Cost Net of Accumulated Depreciation	3,502,113	3,476,178
Investments in real estate partnerships (note 4)	306,206	333,167
Net real estate investments	3,808,319	3,809,345
Cash and cash equivalents	36,856	113,776
Restricted cash	3,767	8,013
Accounts receivable, net of allowance for doubtful accounts of $5,295 and $4,523 at December 31, 2015 and 2014, respectively	32,292	30,999
Straight-line rent receivable, net of reserve of $1,365 and $652 at December 31, 2015 and 2014, respectively	63,392	55,768
Notes receivable (note 5)	10,480	12,132
Deferred Costs	79,619	71,502
Acquired lease intangible assets, less accumulated amortization of $45,639 and $36,112 at December 31, 2015 and 2014, respectively (note 6)	105,380	52,365
Assets Held-in-trust	29,093	28,134
Other assets	21,876	15,136
Total assets	4,191,074	4,197,170
Liabilities:
Notes payable (note 9)	1,707,478	1,946,357
Unsecured Debt	165,000	75,000
Accounts payable and other liabilities	164,515	181,197
Acquired lease intangible liabilities, less accumulated accretion of $17,555 and $13,993 at December 31, 2015 and 2014, respectively (note 6)	42,034	32,143
Tenants’ security and escrow deposits and prepaid rent	29,427	25,991
Total liabilities	2,108,454	2,260,688
Commitments and contingencies (notes 16 and 17)	0	0
Stockholders’ equity (notes 12 and 13):
Preferred stock, $0.01 par value per share, 30,000,000 shares authorized; 13,000,000 Series 6 and 7 shares issued and outstanding at December 31, 2013 and December 31, 2012, with liquidation preferences of $25 per share	325,000	325,000
Common stock $0.01 par value per share,150,000,000 shares authorized; 97,212,638 and 94,108,061 shares issued at December 31, 2015 and 2014, respectively	972	941
Treasury Stock, Value	19,658	19,382
Additional paid in capital	2,742,508	2,540,153
Accumulated other comprehensive loss	(58,693)	(57,748)
Distributions in excess of net income	(936,020)	(882,372)
Total stockholders’ equity	2,054,109	1,906,592
Noncontrolling interests (note 12):
Exchangeable operating partnership units, aggregate redemption value of $7,676 and $8,348 at December 31, 2013 and 2012, respectively	(1,975)	(1,914)
Limited partners’ interests in consolidated partnerships	30,486	31,804
Total noncontrolling interests	28,511	29,890
Total equity	2,082,620	1,936,482
Total liabilities and equity	4,191,074	4,197,170
Partnership Interest [Member]
Real estate investments at cost (notes 2 and 3):
Land	1,432,468	1,380,211
Buildings and improvements	2,896,396	2,790,137
Properties in development	217,036	239,538
Gross real estate investments at cost	4,545,900	4,409,886
Less: accumulated depreciation	1,043,787	933,708
Total Cost Net of Accumulated Depreciation	3,502,113	3,476,178
Investments in real estate partnerships (note 4)	306,206	333,167
Net real estate investments	3,808,319	3,809,345
Cash and cash equivalents	36,856	113,776
Restricted cash	3,767	8,013
Accounts receivable, net of allowance for doubtful accounts of $5,295 and $4,523 at December 31, 2015 and 2014, respectively	32,292	30,999
Straight-line rent receivable, net of reserve of $1,365 and $652 at December 31, 2015 and 2014, respectively	63,392	55,768
Notes receivable (note 5)	10,480	12,132
Deferred Costs	79,619	71,502
Acquired lease intangible assets, less accumulated amortization of $45,639 and $36,112 at December 31, 2015 and 2014, respectively (note 6)	105,380	52,365
Assets Held-in-trust	29,093	28,134
Other assets	21,876	15,136
Total assets	4,191,074	4,197,170
Liabilities:
Notes payable (note 9)	1,707,478	1,946,357
Unsecured Debt	165,000	75,000
Accounts payable and other liabilities	164,515	181,197
Acquired lease intangible liabilities, less accumulated accretion of $17,555 and $13,993 at December 31, 2015 and 2014, respectively (note 6)	42,034	32,143
Tenants’ security and escrow deposits and prepaid rent	29,427	25,991
Total liabilities	2,108,454	2,260,688
Commitments and contingencies (notes 16 and 17)	0	0
Stockholders’ equity (notes 12 and 13):
Preferred Units General Partner	325,000	325,000
General partner; 97,212,638 and 94,108,061 units outstanding at December 31, 2015 and 2014, respectively	1,787,802	1,639,340
Limited Partners' Capital Account	(1,975)	(1,914)
Accumulated other comprehensive loss	(58,693)	(57,748)
Total partners’ capital	2,052,134	1,904,678
Noncontrolling interests (note 12):
Limited partners’ interests in consolidated partnerships	30,486	31,804
Total noncontrolling interests	30,486	31,804
Total equity	2,082,620	1,936,482
Total liabilities and equity	$ 4,191,074	$ 4,197,170