Changes in Outstanding Common Stock (Detail)	1 Months Ended		12 Months Ended						1 Months Ended		12 Months Ended
	Oct. 24, 2011	Jun. 07, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Common Stock	Dec. 31, 2011 Common Stock	Dec. 31, 2010 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, 2012 Series B Subordinated Non-Voting Cumulative Redeemable Preferred Stock	Dec. 31, 2011 Series B Subordinated Non-Voting Cumulative Redeemable Preferred Stock	Dec. 31, 2010 Series B Subordinated Non-Voting Cumulative Redeemable Preferred Stock
Capital Unit [Line Items]
Shares outstanding, beginning balance			41,078,200	30,972,353	30,350,792
Common stock issued through conversion of OP Units			374,907	328,353	482,620
Common stock issued through exercise of options			80,000	172,384	33,767
Common stock issued through stock grants			88,999	108,332	121,665
Common stock issued through ESPP and Dividend Reinvestment Plan			15,554	15,152	20,841
Common stock repurchased and retired			(41,005)	(4,150)	(37,332)
Common stock issued through stock offering		6,037,500	0	6,037,500	0
Shares outstanding, ending balance			41,596,655	41,078,200	30,972,353
Stock issued for acquisition	3,162,069					0	1,708,276	0	286,207	1,453,793	0	1,740,000	0