Total Equity and its Components (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended																						6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Common Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Jun. 30, 2012 Common Stock [Member]	Dec. 31, 2011 Common Stock [Member]	Jun. 30, 2013 Additional Paid-in Capital [Member]	Dec. 31, 2012 Additional Paid-in Capital [Member]	Jun. 30, 2012 Additional Paid-in Capital [Member]	Dec. 31, 2011 Additional Paid-in Capital [Member]	Jun. 30, 2013 Accumulated Distributions in Excess of Net Income	Dec. 31, 2012 Accumulated Distributions in Excess of Net Income	Jun. 30, 2012 Accumulated Distributions in Excess of Net Income	Dec. 31, 2011 Accumulated Distributions in Excess of Net Income	Jun. 30, 2013 Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2012 Accumulated Other Comprehensive Income (Loss) [Member]	Jun. 30, 2012 Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2011 Accumulated Other Comprehensive Income (Loss) [Member]	Jun. 30, 2013 Noncontrolling Interest [Member]	Dec. 31, 2012 Noncontrolling Interest [Member]	Jun. 30, 2012 Noncontrolling Interest [Member]	Dec. 31, 2011 Noncontrolling Interest [Member]	Jun. 30, 2013 Additional Paid-in Capital [Member]	Jun. 30, 2012 Additional Paid-in Capital [Member]	Jun. 30, 2013 Common Stock [Member]	Jun. 30, 2012 Common Stock [Member]	Jun. 30, 2013 Accumulated Other Comprehensive Income (Loss) [Member]	Jun. 30, 2012 Accumulated Other Comprehensive Income (Loss) [Member]	Jun. 30, 2013 Noncontrolling Interest [Member]	Jun. 30, 2012 Noncontrolling Interest [Member]	Jun. 30, 2013 Accumulated Distributions in Excess of Net Income	Jun. 30, 2012 Accumulated Distributions in Excess of Net Income
Stockholders Equity Note [Line Items]
Total Equity			$ 945,110	$ 743,462	$ 427	$ 422	$ 410	$ 389	$ 1,569,090	$ 1,542,999	$ 1,494,172	$ 1,375,623	$ (582,884)	$ (603,315)	$ (624,304)	$ (621,833)	$ (6,336)	$ (26,054)	$ (30,891)	$ (35,848)	$ 31,500	$ 31,058	$ 26,576	$ 25,131
Net income	61,028	29,472	83,033	54,540																											2,764	2,490
Net Income (Loss) Attributable to Parent	59,089	28,160	80,269	52,050																													80,269	52,050
Other comprehensive income - derivative instruments (cash flow hedges)			20,399	5,199																									19,718	4,957	681	242
Issuance and registration of common shares			24,969	120,150																					24,965	120,130	4	20
Shares repurchased and retired			673	1,640																					673	1,640	0	0
Shares issued in exchange for units			0	0																					(442)	(2,515)	(1)	(1)			(443)	(2,516)
Redeemable stock fair market value			431	375																													431	375
Adjustment for Noncontrolling Interest Ownership in operating partnership			0	0																					(186)	(3,687)					(186)	(3,687)
Amortization of unearned compensation			1,171	1,231																					1,171	1,231
Total Equity	1,011,797	865,963	1,011,797	865,963	427	422	410	389	1,569,090	1,542,999	1,494,172	1,375,623	(582,884)	(603,315)	(624,304)	(621,833)	(6,336)	(26,054)	(30,891)	(35,848)	31,500	31,058	26,576	25,131
Dividends on common stock ($.6950 and $.6600 for the 3 months ended March 31, 2013 and 2012)			59,407	54,146																											0	0	59,407	54,146
Dividends on noncontrolling interest units ($.6950 and $.6600 for the 3 months ended March 31, 2013 and 2012)			$ 2,374	$ 2,458																											$ 2,374	$ 2,458