Changes in Outstanding Common Stock (Detail)	1 Months Ended			12 Months Ended				1 Months Ended		12 Months Ended
	Oct. 24, 2011	Jun. 07, 2011	Jun. 30, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Common Stock	Dec. 23, 2011 Series B Subordinated Non-Voting Cumulative Redeemable Preferred Stock	Oct. 24, 2011 Series B Subordinated Non-Voting Cumulative Redeemable Preferred Stock	Dec. 31, 2011 Series B Subordinated Non-Voting Cumulative Redeemable Preferred Stock
Capital Unit [Line Items]
Shares outstanding, beginning balance				30,972,353	30,350,792	25,051,322
Common stock issued through conversion of OP Units				328,353	482,620	448,501
Common stock issued through exercise of options				172,384	33,767	213,721
Common stock issued through stock grants				108,332	121,665	27,000
Common stock issued through ESPP and Dividend Reinvestment Plan				15,152	20,841	34,769
Common stock repurchased and retired				(4,150)	(37,332)	(24,521)
Common stock issued through stock offering		6,037,500	4,600,000	6,037,500		4,600,000
Shares outstanding, ending balance				41,078,200	30,972,353	30,350,792
Stock issued for acquisition	3,162,069						1,708,276	286,207	1,453,793	1,740,000