Combined Consolidated Statements of Changes in Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in-Capital	Distributions in excess of net earnings	Accumulated Other Comprehensive Income	Total Noncontrolling Interests	Operating Partnership	Consolidated Joint Venture
Balance at Dec. 31, 2011	$ 1,833,988	$ 1,063	$ 1,835,011	$ (18,960)	$ (1,782)	$ 18,656	$ 11,486	$ 7,170
Balance (in shares) at Dec. 31, 2011		106,279,049
Increase (Decrease) in Owners' Equity
Net income	27,399			27,568		(169)	283	(452)
Unrealized loss on interest rate derivative	764
Issuance of restricted stock		4	(4)
Issuance of restricted stock (in shares)		436,646
Amortization of share based compensation	5,763		5,763
Share grants to trustees	120		120
Share grants to trustees (in shares)		6,466
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock	(1,695)		(1,695)
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock (in shares)		(94,918)
Forfeiture of restricted stock (in shares)		(26,878)
Distributions on common shares and units	(53,386)			(52,944)		(442)	(442)
Balance at Sep. 30, 2012	1,812,953	1,067	1,839,195	(44,336)	(1,018)	18,045	11,327	6,718
Balance (in shares) at Sep. 30, 2012		106,600,365
Balance at Dec. 31, 2012	1,807,911	1,066	1,841,449	(52,681)		18,077	11,311	6,766
Balance (in shares) at Dec. 31, 2012		106,565,516
Increase (Decrease) in Owners' Equity
Net income	86,497			85,476		1,021	700	321
Unrealized loss on interest rate derivative	(11,429)				(11,429)
Proceeds from sale of common stock, net	327,545	159	327,386
Proceeds from sale of common stock, net (in shares)		15,870,000
Issuance of restricted stock		3	(3)
Issuance of restricted stock (in shares)		377,830
Amortization of share based compensation	9,691		9,691
Share grants to trustees	96		96
Share grants to trustees (in shares)		4,202
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock	(2,871)	(1)	(2,870)
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock (in shares)		(125,698)
Forfeiture of restricted stock (in shares)		(4,217)
Distributions on common shares and units	(76,636)			(76,086)		(550)	(550)
Balance at Sep. 30, 2013	$ 2,140,804	$ 1,227	$ 2,175,749	$ (43,291)	$ (11,429)	$ 18,548	$ 11,461	$ 7,087
Balance (in shares) at Sep. 30, 2013		122,687,633