CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Statement of Cash Flows [Abstract]
Net loss	$ (32,848)	$ (12,713)	$ (129,567)
Depreciation	119,441	125,426	132,347
Amortization	12,057	3,981	12,907
Straight-line rent adjustments	2,686	2,602	1,874
Provision for doubtful accounts	1,763	1,357	2,510
Amortization of deferred compensation	5,709	6,035	6,284
Loss on hedge ineffectiveness	0	143	512
Gain on sales of interests in real estate and non-operating real estate, net	7,448	23,402	12,621
Equity in income of partnerships in excess of distributions	3,200	3,705	2,312
Amortization of historic tax credits	1,768	1,768	1,589
Impairment of assets and expensed project costs	55,793	62,603	140,790
Net change in other assets	5,652	(4,566)	(5,337)
Net change in other liabilities	(4,752)	(12,312)	(17,063)
Net cash provided by operating activities	136,409	147,609	135,661
Cash proceeds from sales of real estate investments	77,778	154,758	52,956
Proceeds from Sale of Equity Method Investments	30,265
Proceeds from (Payments for) Other Financing Activities	35,221
Investments in consolidated real estate acquisitions	0	0	319,986
Additions to construction in progress	116,550	88,161	30,684
Investments in real estate improvements	51,949	49,942	52,790
Additions to leasehold improvements	683	522	486
Investments in partnerships	73,434	14,910	25,046
Capitalized leasing costs	6,066	6,101	6,255
Increase in cash escrows	(1,457)	473	1,996
Cash distributions from partnerships in excess of equity in income	5,682	7,322	5,188
Net cash (used in) provided by investing activities	(98,279)	1,971	(379,099)
Proceeds from Issuance of Preferred Stock and Preference Stock	286,847
Proceeds from Issuance of Unsecured Debt	0	0	120,000
Net borrowings from 2013 Revolving Facility	(56,000)	(82,000)	(215,000)
Proceeds from mortgage loans	0	139,000	272,044
Repayment of mortgage loans	150,000	280,327	272,650
Principal installments on mortgage loans	17,945	17,868	20,761
Payment of deferred financing costs	71	3,337	3,754
Common shares issued	2,085	1,288	1,393
Dividends paid to common shareholders	58,651	58,372	58,085
Dividends paid to preferred shareholders	27,403	15,848	15,848
Distributions paid to Operating Partnership unit holders and noncontrolling interest	6,970	6,991	5,703
Value of shares issued under equity incentive plans, net of shares retired	1,477	2,177	5,776
Redeemable Noncontrolling Interest, Equity, Preferred, Redemption Value	(115,000)
Net cash (used in) provided by financing activities	(32,585)	(162,632)	225,860
Net change in cash and cash equivalents	5,545	(13,052)	(17,578)
Cash and cash equivalents	$ 15,348	$ 9,803	$ 22,855