Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Shares Outstanding
Weighted average common shares - basic	42,354	39,505
Weighted average partnership units outstanding	1,715	1,936
Effect of dilutive securities	80	102
Weighted average common shares - diluted	44,149	41,543
Calculation of Earnings per Share - basic
Income from continuing operations	$ 22,005	$ 15,209
Income from continuing operations attributable to noncontrolling interests	(825)	(691)
Income from continuing operations allocated to unvested restricted shares	(20)	(16)
Income from continuing operations available for common shareholders, adjusted	21,160	14,502
Income from discontinued operations	0	(9,859)
Income from discontinued operations attributable to noncontrolling interest	0	(488)
Income from discontinued operations allocated to unvested restricted shares	0	(11)
Income from discontinued operations available for common shareholders, adjusted	0	9,360
Weighted average common shares - basic	42,354	39,505
Earnings per share - basic	$ 0.50	$ 0.60
Calculation of Earnings per Share - diluted
Net income available for common shareholders	21,180	23,890
Net income attributable to noncontrolling interests	825	1,178
Adjusted net income from continuing operations available for common shareholders	$ 22,005	$ 15,209
Weighted average common shares - diluted	44,149	41,543
Earnings per share - diluted	$ 0.50	$ 0.60