CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY AND COMPREHENSIVE INCOME (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Parent	Noncontrolling Interest
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 (in Shares)		11,000
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0	0	49	0	0	49	(49)
Issuance of OP Units to Acquire Real Estate	0
Dividends declared ($0.54 per Common Share)	(22,514)	0	0	0	(21,776)	(21,776)	(738)
Vesting of employee Restricted Share and LTIP awards (in Shares)		95,000
Vesting of employee Restricted Share and LTIP awards	3,218	0	389	0	0	389	2,829
Common Shares issued under Employee Share Purchase Plan (in Shares)		4,000
Common Shares issued under Employee Share Purchase Plan	68	0	68	0	0	68	0
Issuance of LTIP Unit awards to employees	2,441	0	0	0	0	0	2,441
Issuance of Common Shares to trustees (in Shares)		8,000
Issuance of Common Shares to trustees	171	0	171	0	0	171	0
Exercise of Share options (in Shares)		1,000
Exercise of Share options	7	0	7	0	0	7	0
Employee Restricted Shares cancelled (in Shares)		(40,000)
Employee Restricted Shares cancelled	(724)	0	(724)	0	0	(724)	0
Noncontrolling interest distributions	(815)	0	0	0	0	0	(815)
Noncontrolling Interest contributions	43,646	0	0	0	0	0	43,646
Balance before adjustment towards comprehensive income (in Shares)		40,333,000
Balance before adjustment towards comprehensive income	613,020	40	303,783	(2,857)	(4,570)	296,396	316,624
Comprehensive (loss) income:
Net income	39,340	0	0	0	43,668	43,668	(4,328)
Unrealized loss on valuation of swap agreements	(5,209)	0	0	(3,265)	0	(3,265)	(1,944)
Reclassification of realized interest on swap agreements	2,398	0	0	1,891	0	1,891	507
Total comprehensive (loss) income	36,529	0	0	(1,374)	43,668	42,294	(5,765)
Balance at Sep. 30, 2011	649,549	40	303,783	(4,231)	39,098	338,690	310,859
Balance (in Shares) at Sep. 30, 2011		40,333,000
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 (in Shares)		171,000
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0	0	2,711	0	0	2,711	(2,711)
Issuance of Common Shares, net of issuance costs (in Shares)		4,332,000
Issuance of Common Shares, net of issuance costs	98,312	4	98,308	0	0	98,312	0
Issuance of OP Units to Acquire Real Estate	2,279	0	0	0	0	0	2,279
Dividends declared ($0.54 per Common Share)	(25,324)	0	0	0	(24,477)	(24,477)	(847)
Vesting of employee Restricted Share and LTIP awards (in Shares)		44,000
Vesting of employee Restricted Share and LTIP awards	2,707	0	128	0	0	128	2,579
Common Shares issued under Employee Share Purchase Plan (in Shares)		3,000
Common Shares issued under Employee Share Purchase Plan	59	0	59	0	0	59	0
Issuance of LTIP Unit awards to employees	2,577	0	0	0	0	0	2,577
Issuance of Common Shares to trustees (in Shares)		0
Issuance of Common Shares to trustees	280	0	280	0	0	280	0
Exercise of Share options (in Shares)		11,000
Exercise of Share options	160	0	160	0	0	160	0
Employee Restricted Shares cancelled (in Shares)		(8,000)
Employee Restricted Shares cancelled	(150)	0	(150)	0	0	(150)	0
Noncontrolling interest distributions	(62,645)	0	0	0	0	0	(62,645)
Noncontrolling Interest contributions	122,309	0	0	0	0	0	122,309
Balance before adjustment towards comprehensive income (in Shares)		47,139,000
Balance before adjustment towards comprehensive income	909,873	47	450,163	(3,913)	14,840	461,137	448,736
Comprehensive (loss) income:
Net income	20,652	0	0	0	18,429	18,429	2,223
Unrealized loss on valuation of swap agreements	(3,870)	0	0	(2,212)	0	(2,212)	(1,658)
Reclassification of realized interest on swap agreements	1,964	0	0	1,362	0	1,362	602
Total comprehensive (loss) income	18,746	0	0	(850)	18,429	17,579	1,167
Balance at Sep. 30, 2012	$ 928,619	$ 47	$ 450,163	$ (4,763)	$ 33,269	$ 478,716	$ 449,903
Balance (in Shares) at Sep. 30, 2012	47,138,544	47,139,000