Share and Unit Information - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended					9 Months Ended				3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Mar. 02, 2012	Sep. 30, 2013 At Market A T M Programs [Member]	Sep. 30, 2012 At Market A T M Programs [Member]	Sep. 30, 2013 At The Market ATM Programs [Member]	Sep. 30, 2012 At The Market ATM Programs [Member]	Mar. 31, 2012 Initial Public Offering [Member]	Sep. 30, 2013 Noncontrolling Interest [Member]	Sep. 30, 2012 Noncontrolling Interest [Member]
Stockholders Equity Note [Line Items]
Limited Partners' Capital Account, Units Outstanding													1,701,955	1,774,547
Common stock, shares outstanding	42,744,978	41,925,288	42,744,978	41,925,288		42,316,398
Total common shares and operating partnership units outstanding	44,446,933	43,699,835	44,446,933	43,699,835
Common stock shares, outstanding option	0		0
Agreement to sell common stock with financial service companies, shares					4,500,000
Stock Issued During Period, Shares, New Issues								365,011	812,911	4,134,989
proceeds from issuance of common stock, net of applicable fees										$ 24,800,000	$ 53,700,000	$ 120,000,000
Proceeds from Issuance of common stock			25,038,000	173,960,000						25,100,000	54,500,000	124,100,000
Shares Sold On Underwritten Public Offering							1,955,000
Common stock issued, Dividend and Distribution Reinvestment and Share Purchase Program	435	122	764	451
Proceeds from Issuance of common stock, Dividend and Distribution Reinvestment and Share Purchase Program	$ 28,000	$ 8,000	$ 50,000	$ 30,000
Treasury Stock, Shares, Acquired			4,805	15,565