CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Total Common Shareholders’ Equity	Noncontrolling Interests
Balance at Dec. 31, 2009	$ 532,477	$ 40	$ 299,014	$ (2,994)	$ 16,125	$ 312,185	$ 220,292
Balance (in Shares) at Dec. 31, 2009		39,787,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership			3,240			3,240	(3,240)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		365,000
Issuance of OP Units to acquire real estate	0
Vesting of employee Restricted Share and LTIP awards	3,838		2,060			2,060	1,778
Vesting of employee Restricted Share and LTIP awards (in Shares)		133,000
Dividends declared	(29,699)				(28,976)	(28,976)	(723)
Exercise of options	109		109			109	0
Exercise of options (in Shares)		7,000
Common Shares issued under Employee Share Purchase Plan	100	0	100	0	0	100	0
Common Shares issued under Employee Share Purchase Plan (in Shares)		6,184
Issuance of Common Shares to Trustees	266		266			266
Issuance of Common Shares to Trustees (in Shares)		13,000
Employee Restricted Shares canceled	(966)		(966)			(966)
Employee Restricted Shares cancelled (in Shares)		(57,000)
Noncontrolling interest distributions	(2,892)						(2,892)
Noncontrolling interest contributions	33,556						33,556
Balance before adjustment toward comprehensive income	536,789	40	303,823	(2,994)	(12,851)	288,018	248,771
Balance before adjustment toward comprehensive income (in Shares)		40,254,000
Comprehensive income (loss):
Net income	50,667				30,057	30,057	20,610
Unrealized loss on valuation of swap agreements	(2,683)			(2,329)	0	(2,329)	(354)
Reclassification of realized interest on swap agreements	2,749			2,466	0	2,466	283
Total comprehensive income	50,733			137	30,057	30,194	20,539
Balance at Dec. 31, 2010	587,522	40	303,823	(2,857)	17,206	318,212	269,310
Balance (in Shares) at Dec. 31, 2010		40,254,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership			56			56	(56)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		11,000
Issuance of Common Shares, net of issuance costs	44,660	2	44,658			44,660
Issuance of Common Shares, net of issuance costs (in Shares)		2,250,000
Issuance of OP Units to acquire real estate	0
Vesting of employee Restricted Share and LTIP awards	4,032	1	481			482	3,550
Vesting of employee Restricted Share and LTIP awards (in Shares)		96,000
Dividends declared	(30,428)				(29,444)	(29,444)	(984)
Exercise of options	16		16			16
Exercise of options (in Shares)		2,000
Common Shares issued under Employee Share Purchase Plan	93		93			93
Common Shares issued under Employee Share Purchase Plan (in Shares)		4,886
Issuance of LTIP Unit awards to employees	2,441						2,441
Issuance of Common Shares to Trustees	264		264			264
Issuance of Common Shares to Trustees (in Shares)		8,000
Employee Restricted Shares canceled	(724)		(724)			(724)
Employee Restricted Shares cancelled (in Shares)		(40,000)
Noncontrolling interest distributions	(7,697)						(7,697)
Noncontrolling interest contributions	117,945						117,945
Balance before adjustment toward comprehensive income	718,124	43	348,667	(2,857)	(12,238)	333,615	384,509
Balance before adjustment toward comprehensive income (in Shares)		42,586,000
Comprehensive income (loss):
Net income	53,715				51,555	51,555	2,160
Unrealized loss on valuation of swap agreements	(5,611)			(3,461)		(3,461)	(2,150)
Reclassification of realized interest on swap agreements	3,081			2,405		2,405	676
Total comprehensive income	51,185			(1,056)	51,555	50,499	686
Balance at Dec. 31, 2011	769,309	43	348,667	(3,913)	39,317	384,114	385,195
Balance (in Shares) at Dec. 31, 2011	42,586,376	42,586,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership			5,880			5,880	(5,880)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		334,000
Issuance of Common Shares, net of issuance costs	226,721	9	226,712			226,721
Issuance of Common Shares, net of issuance costs (in Shares)		9,510,000
Issuance of OP Units to acquire real estate	2,279						2,279
Vesting of employee Restricted Share and LTIP awards	3,640		192			192	3,448
Vesting of employee Restricted Share and LTIP awards (in Shares)		44,000
Dividends declared	(34,994)				(33,896)	(33,896)	(1,098)
Exercise of options	187		187			187
Exercise of options (in Shares)		12,636
Common Shares issued under Employee Share Purchase Plan	75		75			75
Common Shares issued under Employee Share Purchase Plan (in Shares)		3,829
Issuance of LTIP Unit awards to employees	2,577						2,577
Issuance of Common Shares to Trustees	384		384			384
Issuance of Common Shares to Trustees (in Shares)		0
Employee Restricted Shares canceled	(172)		(172)			(172)
Employee Restricted Shares cancelled (in Shares)		(9,000)
Noncontrolling interest distributions	(160,663)						(160,663)
Noncontrolling interest contributions	172,228						172,228
Balance before adjustment toward comprehensive income	981,571	52	581,925	(3,913)	5,421	583,485	398,086
Balance before adjustment toward comprehensive income (in Shares)		52,482,000
Comprehensive income (loss):
Net income	89,936				39,706	39,706	50,230
Unrealized loss on valuation of swap agreements	(3,519)			(1,815)		(1,815)	(1,704)
Reclassification of realized interest on swap agreements	2,268			1,421		1,421	847
Total comprehensive income	88,685			(394)	39,706	39,312	49,373
Balance at Dec. 31, 2012	$ 1,070,256	$ 52	$ 581,925	$ (4,307)	$ 45,127	$ 622,797	$ 447,459
Balance (in Shares) at Dec. 31, 2012	52,482,598	52,482,000