Condensed Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Distributions in Excess of Net Income [Member]	Stockholders' Investment [Member]	Nonredeemable Noncontrolling Interests [Member]
Net Income (Loss) in Statement on Equity	$ 126,761	$ 0	$ 0	$ 0	$ 0	$ 121,761	$ 121,761
Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Nonredeemable								$ 5,000
Net Income (Loss) Attributable to Parent	121,761
Beginning balance at Dec. 31, 2012	642,953	169,602	107,660	690,024	(86,840)	(260,104)	620,342	22,611
Common stock issued pursuant to:
Common stock offering, net of issuance costs	826,233	0	85,507	740,726	0	0	826,233	0
Restricted stock grants, net of amounts withheld for income taxes					0	0		0
Share-based Compensation	(806)	0	111	(917)			(806)
Amortization of stock options and restricted stock, net of forfeitures	1,898	0	(42)	1,940	0	0	1,898	0
Distributions to nonredeemable noncontrolling interests	(26,040)	0	0	0	0	0	0	(26,040)
Preferred Stock Redemption	(74,827)	(74,827)	0	(10,822)	0	10,822	(74,827)	0
Cash preferred dividends paid	(10,008)	0	0	0	0	(10,008)	(10,008)	0
Cash common dividends paid	(27,192)	0	0	0	0	(27,192)	(27,192)	0
Ending balance at Dec. 31, 2013	1,458,972	$ 94,775	$ 193,236	$ 1,420,951	$ (86,840)	(164,721)	1,457,401	1,571
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	53,008					52,004	52,004
Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Nonredeemable								1,004
Net Income (Loss) Attributable to Parent	52,004
Common stock issued pursuant to:
Director stock grants	321,896	$ 0	$ 26,700	$ 295,196	$ 0	0	321,896	0
Restricted stock grants, net of amounts withheld for income taxes					0	0		0
Share-based Compensation	(550)	0	156	(706)			(550)
Amortization of stock options and restricted stock, net of forfeitures	1,992	0	(9)	2,001	0	0	1,992	0
Distributions to nonredeemable noncontrolling interests	(2,575)	0	0	0	0	0	0	(2,575)
Preferred Stock Redemption	(94,775)	(94,775)	0	3,530	0	(3,530)	(94,775)	0
Cash preferred dividends paid	(2,955)	0	0	0	0	(2,955)	(2,955)	0
Cash common dividends paid	(61,555)	0	0	0	0	(61,555)	(61,555)	0
Ending balance at Dec. 31, 2014	1,673,458	0	$ 220,083	$ 1,720,972	$ (86,840)	(180,757)	1,673,458	0
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	125,629	0					125,518
Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Nonredeemable								111
Net Income (Loss) Attributable to Parent	125,518
Common stock issued pursuant to:
Restricted stock grants, net of amounts withheld for income taxes					$ 0	0		0
Share-based Compensation	72	0	$ 173	$ (245)			72
Amortization of stock options and restricted stock, net of forfeitures	1,473	0	0	1,473	0	0	1,473	0
Distributions to nonredeemable noncontrolling interests	(111)	0	0	0	0	0	0	(111)
Preferred Stock Redemption	0
Stock Repurchased During Period, Value	(47,790)	0	0	0	(47,790)	0	(47,790)	0
Cash common dividends paid	(69,196)	0	0	0	0	(69,196)	(69,196)	0
Ending balance at Dec. 31, 2015	1,683,415	0	220,256	1,722,224	(134,630)	(124,435)	1,683,415	0
Common stock issued pursuant to:
Stock Issued During Period, Value, Other	$ 24	$ 0	$ 0	$ 24	$ 0	$ 0	$ 24	$ 0