Condensed Consolidated Statements of Equity (USD $) In Thousands, unless otherwise specified	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Treasury Stock	Distributions in Excess of Net Income	Stockholders' Investment	Nonredeemable Noncontrolling Interests
Beginning Balance at Dec. 31, 2013	$ 1,458,972	$ 94,775	$ 193,236	$ 1,420,951	$ (86,840)	$ (164,721)	$ 1,457,401	$ 1,571
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	7,132	0	0	0	0	6,977	6,977	155
Common stock issued pursuant to:
Stock Issued During Period, Value, Stock Options Exercised	(20)	0	3	(23)	0	0	(20)	0
Stock Issued During Period, Value, New Issues	98,564	0	8,700	89,864	0	0	98,564	0
Restricted stock grants, net of amounts withheld for income taxes	(916)	0	54	(970)	0	0	(916)	0
Amortization of stock options and restricted stock, net of forfeitures	587	0	0	587	0	0	587	0
Distributions to noncontrolling interests	(153)	0	0	0	0	0	0	(153)
Preferred dividends paid	(1,777)	0	0	0	0	(1,777)	(1,777)	0
Common dividends paid	(14,231)	0	0	0	0	(14,231)	(14,231)	0
Ending Balance at Mar. 31, 2014	1,548,158	94,775	201,993	1,510,409	(86,840)	(173,752)	1,546,585	1,573
Beginning Balance at Dec. 31, 2014	1,673,458	0	220,083	1,720,972	(86,840)	(180,757)	1,673,458	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	7,203	0	0	0	0	7,203	7,203	0
Common stock issued pursuant to:
Stock Issued During Period, Value, Stock Options Exercised	(14)	0	1	(15)	0	0	(14)	0
Restricted stock grants, net of amounts withheld for income taxes	(838)	0	88	(926)	0	0	(838)	0
Amortization of stock options and restricted stock, net of forfeitures	475	0	0	475	0	0	475	0
Common dividends paid	(17,349)	0	0	0	0	(17,349)	(17,349)	0
Ending Balance at Mar. 31, 2015	$ 1,662,935	$ 0	$ 220,172	$ 1,720,506	$ (86,840)	$ (190,903)	$ 1,662,935	$ 0