Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in-Capital	Retained Earnings (Distributions in excess of net earnings)	Accumulated Other Comprehensive Loss	Total Noncontrolling Interests	Operating Partnership	Consolidated Joint Venture	Series A Cumulative Preferred Stock [Member]
Net Income (Loss) Attributable to Parent	$ 218,221
Balance (in shares) at Dec. 31, 2014		131,964,706
Balance at Dec. 31, 2014	2,378,484	$ 1,319	$ 2,419,731	$ (46,415)	$ (13,644)		$ 11,198	$ 6,295
Increase (Decrease) in Equity
Net income (loss)	219,812			218,221			1,514	77
Unrealized gain (loss) on interest rate derivatives	(2,958)				(2,958)
Number of shares acquired as part of a share repurchase program (in shares)		(8,044,372)
Shares acquired as part of a share repurchase program	(225,186)	$ (80)	(225,106)
Issuance of restricted stock (in shares)		1,126,431
Issuance of restricted stock	0	$ 11	(11)
Amortization of share-based compensation	13,002		13,002
Share grants to trustees (in shares)		5,008
Share grants to trustees	132		132
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock (in shares)		(403,722)
Shares acquired to satisfy statutory minimum federal and state tax obligations on vesting restricted stock	(12,020)	$ (4)	(12,016)
Forfeiture of restricted stock (in shares)		(12,376)
Restricted Stock Award, Forfeitures	0
Distribution to joint venture partner	(195)							(195)
Distributions on common shares and units	(170,547)			(169,367)			(1,180)
Balance (in shares) at Dec. 31, 2015		124,635,675
Balance at Dec. 31, 2015	2,200,524	$ 1,246	2,195,732	2,439	(16,602)		11,532	6,177
Increase (Decrease) in Equity
Preferred Stock Dividends and Other Adjustments	0
Net Income (Loss) Attributable to Parent	200,352
Net income (loss)	201,314			200,352			907	55
Unrealized gain (loss) on interest rate derivatives	$ 11,700				11,700
Redemption of Operating Partnership units, shares		335,250
Number of shares acquired as part of a share repurchase program (in shares)	(610,607)	(610,607)
Shares acquired as part of a share repurchase program	$ (13,271)	$ (6)	(13,265)
Issuance of restricted stock (in shares)		672,821
Issuance of restricted stock	0	$ 7	(7)
Amortization of share-based compensation	5,990		5,990
Share grants to trustees (in shares)		2,554
Share grants to trustees	57		57
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock (in shares)		(244,015)
Shares acquired to satisfy statutory minimum federal and state tax obligations on vesting restricted stock	(5,502)	$ (2)	(5,500)
Forfeiture of restricted stock (in shares)		(427,500)
Restricted Stock Award, Forfeitures	0	$ (4)	4
Distribution to joint venture partner	(259)							(259)
Distributions on common shares and units	(165,276)			(164,542)			(734)
Balance (in shares) at Dec. 31, 2016		124,364,178
Balance at Dec. 31, 2016	2,235,277	$ 1,244	2,187,333	38,249	(4,902)	$ 0	7,380	5,973
Increase (Decrease) in Equity
Preferred Stock Dividends and Other Adjustments	0
Net Income (Loss) Attributable to Parent	74,835
Net income (loss)	75,739						291	117
Unrealized gain (loss) on interest rate derivatives	$ 13,748				13,748
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares									12,879,475
Stock Issued During Period, Value, Acquisitions									$ 366,936
Number of shares acquired as part of a share repurchase program (in shares)	(122,508)	(122,508)
Shares acquired as part of a share repurchase program	$ (2,610)	$ (1)	(2,609)
Issuance of restricted stock (in shares)		425,076
Issuance of restricted stock	0	$ 4	(4)
Amortization of share-based compensation	10,607		10,607
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock (in shares)		(144,766)
Shares acquired to satisfy statutory minimum federal and state tax obligations on vesting restricted stock	(3,050)	$ (2)	(3,048)
Forfeiture of restricted stock (in shares)		(11,038)
Restricted Stock Award, Forfeitures	0	$ 0	0
Contributions from a noncontrolling interest	117							117
Distributions on common shares and units	(188,110)			(187,278)		0	(832)
Balance (in shares) at Dec. 31, 2017		174,869,046							12,879,475
Balance at Dec. 31, 2017	3,570,278	$ 1,749	$ 3,208,002	$ (82,566)	$ 8,846	$ 44,430	$ 11,181	$ 11,700	$ 366,936
Increase (Decrease) in Equity
Preferred Stock Dividends and Other Adjustments	$ (496)