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 (loss)	41,319			41,298		21	425	(404)
Unrealized gain on interest rate derivatives	1,782
Issuance of restricted stock		4	(4)
Issuance of restricted stock (in shares)		436,646
Amortization of share based compensation-	8,626		8,626
Share grants to trustees	160		160
Share grants to trustees (in shares)		8,530
Shares acquired to satisfy statutory minimum federal and state tax obligations on vesting restricted stock	(2,345)	(1)	(2,344)
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock (in shares)		(131,831)
Forfeiture of restricted stock (in shares)		(26,878)
Distributions on common shares and units	(75,619)			(75,019)		(600)	(600)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	1,782
Balance at Dec. 31, 2012	1,807,911	1,066	1,841,449	(52,681)	0	18,077	11,311	6,766
Balance (in shares) at Dec. 31, 2012		106,565,516
Increase (Decrease) in Owners' Equity
Net income (loss)	114,179			112,921		1,258	718	540
Unrealized gain on interest rate derivatives	(5,941)
Proceeds from sale of common stock, net (in shares)		15,870,000
Proceeds from sale of common stock, net-	327,547	159	327,388
Issuance of restricted stock		3	(3)
Issuance of restricted stock (in shares)		377,830
Amortization of share based compensation-	13,078		13,078
Share grants to trustees	124		124
Share grants to trustees (in shares)		5,357
Shares acquired to satisfy statutory minimum federal and state tax obligations on vesting restricted stock	(4,034)	(2)	(4,032)
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock (in shares)		(173,409)
Forfeiture of restricted stock (in shares)		(5,252)
Distributions on common shares and units	(106,530)			(105,762)		(768)	(768)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	(5,941)
Balance at Dec. 31, 2013	2,146,334	1,226	2,178,004	(45,522)	(5,941)	18,567	11,261	7,306
Balance (in shares) at Dec. 31, 2013		122,640,042
Increase (Decrease) in Owners' Equity
Net income (loss)	136,480			135,441		1,039	868	171
Unrealized gain on interest rate derivatives	(7,703)
Proceeds from sale of common stock, net (in shares)		9,200,000
Proceeds from sale of common stock, net-	232,712	92	232,620
Issuance of restricted stock		3	(3)
Issuance of restricted stock (in shares)		343,887
Amortization of share based compensation-	15,088		15,088
Share grants to trustees	127		127
Share grants to trustees (in shares)		4,347
Shares acquired to satisfy statutory minimum federal and state tax obligations on vesting restricted stock	(6,107)	(2)	(6,105)
Shares acquired to satisfy minimum required federal and state tax withholding on vesting restricted stock (in shares)		(211,983)
Forfeiture of restricted stock (in shares)		(11,587)
Distributions to JV partner	(1,182)							(1,182)
Distributions on common shares and units	(137,265)			(136,334)		(931)	(931)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	(7,703)
Balance at Dec. 31, 2014	$ 2,378,484	$ 1,319	$ 2,419,731	$ (46,415)	$ (13,644)	$ 17,493	$ 11,198	$ 6,295
Balance (in shares) at Dec. 31, 2014		131,964,706