Share and Unit Information - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 02, 2012	Dec. 31, 2011	Aug. 26, 2010	Nov. 05, 2009	Jul. 03, 2008
Stockholders Equity Note [Line Items]
Common stock, shares outstanding	40,940,360	36,545,130		38,959,338
Operating partnership unit outstanding	1,935,708	2,013,393
Total common shares and operating partnership units outstanding	42,876,068	38,558,523
Common stock shares, outstanding option	0	14,907
Agreement to sell common stock with financial service companies, shares					6,000,000	4,000,000	1,350,000
Proceeds from Issuance of common stock	$ 120,135	$ 91,443
Shares Sold On Underwritten Public Offering			1,955,000
Common stock issued, Dividend and Distribution Reinvestment and Share Purchase Program	120	495,236
Proceeds from Issuance of common stock, Dividend and Distribution Reinvestment and Share Purchase Program	8	30,000
Common stock acquired to satisfy tax withholding obligation that arose upon vesting of restricted stock granted	15,565	25,082
At The Market (ATM) Programs
Stockholders Equity Note [Line Items]
Common stock, shares issued		993,799
Proceeds from Issuance of common stock		61,200
Initial Public Offering [Member]
Stockholders Equity Note [Line Items]
Proceeds from Issuance of common stock	$ 120,000