Condensed Consolidated Statements of Equity - USD ($) $ in Thousands	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	9,748	0	0	0	0	9,464	9,464	284
Common stock issued pursuant to:
Stock Granted, Value, Share-based Compensation, Net of Forfeitures	653	0	55	598	0	0	653	0
Stock Issued During Period, Value, Stock Options Exercised	(20)	0	3	(23)	0	0	(20)	0
Stock Issued During Period, Value, New Issues	98,519	0	8,700	89,819	0	0	98,519	0
Restricted stock grants, net of amounts withheld for income taxes	(925)	0	53	(978)	0	0	(925)	0
Amortization of stock options and restricted stock, net of forfeitures	1,059	0	(3)	1,062	0	0	1,059	0
Distributions to noncontrolling interests	(281)	0	0	0	0	0	0	(281)
Preferred Stock Redemption	(94,775)	(94,775)	0	3,530	0	(3,530)	(94,775)	0
Preferred dividends paid	(2,955)	0	0	0	0	(2,955)	(2,955)	0
Common dividends paid	(29,115)	0	0	0	0	(29,115)	(29,115)	0
Ending Balance at Jun. 30, 2014	1,440,880	0	202,044	1,514,959	(86,840)	(190,857)	1,439,306	1,574
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	15,155	0	0	0	0	15,155	15,155	0
Common stock issued pursuant to:
Stock Granted, Value, Share-based Compensation, Net of Forfeitures	765	0	79	686	0	0	765	0
Stock Issued During Period, Value, Stock Options Exercised	(15)	0	4	(19)	0	0	(15)	0
Stock Issued During Period, Value, New Issues				24
Restricted stock grants, net of amounts withheld for income taxes	(821)	0	90	(911)	0	0	(821)	0
Amortization of stock options and restricted stock, net of forfeitures	808	0	0	808	0	0	808	0
Preferred Stock Redemption	0
Common dividends paid	(34,677)	0	0	0	0	(34,677)	(34,677)	0
Ending Balance at Jun. 30, 2015	$ 1,654,697	$ 0	$ 220,256	$ 1,721,560	$ (86,840)	$ (200,279)	$ 1,654,697	$ 0