Share and Unit Information - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended						3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Mar. 02, 2012	Aug. 26, 2010	Jun. 30, 2013 At Market A T M Programs [Member]	Jun. 30, 2013 At Market A T M Programs [Member]	Jun. 30, 2013 At The Market ATM Programs [Member]	Jun. 30, 2013 At The Market ATM Programs [Member]	Mar. 31, 2012 Initial Public Offering [Member]	Jun. 30, 2013 Noncontrolling Interest [Member]	Jun. 30, 2012 Noncontrolling Interest [Member]
Stockholders Equity Note [Line Items]
Limited Partners' Capital Account, Units Outstanding														1,707,660	1,784,208
Common stock, shares outstanding	42,736,134	41,101,427	42,736,134	41,101,427		42,316,398
Total common shares and operating partnership units outstanding	44,443,794	42,885,635	44,443,794	42,885,635
Common stock shares, outstanding option	0		0
Agreement to sell common stock with financial service companies, shares					4,500,000			6,000,000
Stock Issued During Period, Shares, New Issues									39,845	365,011		4,134,989
proceeds from issuance of common stock, net of applicable fees											$ 2,700,000	$ 24,800,000	$ 120,000,000
Proceeds from Issuance of common stock			24,968,000	120,148,000							2,800,000	25,100,000	124,100,000
Shares Sold On Underwritten Public Offering							1,955,000
Common stock issued, Dividend and Distribution Reinvestment and Share Purchase Program	188	209	329	329
Proceeds from Issuance of common stock, Dividend and Distribution Reinvestment and Share Purchase Program	$ 13,000	$ 14,000	$ 22,000	$ 22,000
Treasury Stock, Shares, Acquired			4,582	15,565