Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011
Shares Outstanding
Weighted average common shares - basic	41,405		37,274	40,634		36,612
Weighted average partnership units outstanding	1,781		1,946	1,859		2,009
Effect of dilutive securities	35		80	74		101
Weighted average common shares - diluted	43,221		39,300	42,567		38,722
Calculation of Earnings per Share - basic
Net income available for common shareholders	$ 30,866		$ 13,791	$ 82,916		$ 30,063
Net income allocated to unvested restricted shares	(25)		(18)	(79)		(30)
Net income available for common shareholders, adjusted	30,841		13,773	82,837		30,033
Weighted average common shares - basic	41,405		37,274	40,634		36,612
Earnings per share - basic	$ 0.74		$ 0.37	$ 2.04		$ 0.82
Calculation of Earnings per Share - diluted
Net income available for common shareholders	30,866		13,791	82,916		30,063
Net income attributable to noncontrolling interests	1,212	[1]	660	3,702	[1]	1,223
Adjusted net income available for common shareholders	$ 32,078		$ 14,451	$ 86,618		$ 31,286
Weighted average common shares - diluted	43,221		39,300	42,567		38,722
Earnings per share - diluted	$ 0.74		$ 0.37	$ 2.03		$ 0.81

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