Consolidated Statements of Changes In Equity (USD $)	Total	Common Stock	Paid-in Capital	Cumulative Series Eight Point Zero Three Four Percent Redeemable Perpetual Preferred Stock [Member]	Cumulative Series C Six Point Seven Five Percent Redeemable Perpetual Preferred Stock [Member]	Distributions in Excess of Accumulated Comprehensive Earnings	Non-controlling Interests - Common OP Units	Series B Preferred Stock	Accumulated Other Comprehensive Income
Beginning Balance at Dec. 31, 2009	$ 254,427,000	$ 301,000	$ 456,696,000	$ 0	$ 0	$ (238,467,000)	$ 35,897,000	$ 0	$ 0
Conversion of OP Units to common stock	0	9,000	3,662,000	0	0	0	(3,671,000)	0	0
Issuance of common stock through exercise of options	1,106,000	0	1,106,000	0	0	0	0	0	0
Issuance of common stock through employee stock purchase plan	1,076,000	0	1,076,000	0	0	0	0	0	0
Compensation expenses related to stock options and restricted stock	5,436,000	0	5,436,000	0	0	0	0	0	0
Repurchase of common stock or Common OP Units	(2,054,000)	0	(2,054,000)	0	0	0	0	0	0
Adjustment for Common OP Unitholders in the Operating Partnership	0	0	(751,000)	0	0	0	751,000	0	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	0
Acquisition of non-controlling interests	(1,581,000)	0	(1,449,000)	0	0	0	(132,000)	0	0
Net income	38,354,000
Distributions	(42,509,000)	0	0	0	0	(36,889,000)	(5,620,000)	0	0
Net Income (Loss) Attributable to Parent	44,257,000	0	0	0	0	38,354,000	5,903,000	0	0
Payments for Repurchase of Preferred Stock and Preference Stock	0
Ending Balance at Dec. 31, 2010	260,158,000	310,000	463,722,000	0	0	(237,002,000)	33,128,000	0	0
Conversion of OP Units to common stock	0	4,000	4,063,000	0	0	0	(4,067,000)	0	0
Issuance of common stock through exercise of options	4,571,000	4,000	4,567,000	0	0	0	0	0	0
Issuance of common stock through employee stock purchase plan	913,000	0	913,000	0	0	0	0	0	0
Common stock offering	344,049,000	60,000	343,989,000	0	0	0	0	0	0
Compensation expenses related to stock options and restricted stock	5,762,000	0	5,762,000	0	0	0	0	0	0
Repurchase of common stock or Common OP Units	(1,682,000)	0	(1,682,000)	0	0	0	0	0	0
Adjustment for Common OP Unitholders in the Operating Partnership	0	0	(47,100,000)	0	0	0	47,100,000	0	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(2,547,000)	0	0	0	0	0	0	0	(2,547,000)
Stock issued for Acquisition	224,283,000	17,000	110,478,000	0	0	0	0	113,788,000	0
Redemption of Series B Preferred Stock for Common stock	0	17,000	113,771,000	0	0	0	0	(113,788,000)	0
Net income	22,775,000
Distributions	(62,573,000)	0	0	0	0	(55,794,000)	(6,313,000)	(466,000)	0
Net Income (Loss) Attributable to Parent	26,346,000	0	0	0	0	22,775,000	3,105,000	466,000	0
Payments for Repurchase of Preferred Stock and Preference Stock	0
Ending Balance at Dec. 31, 2011	799,280,000	412,000	998,483,000	0	0	(270,021,000)	72,953,000	0	(2,547,000)
Conversion of OP Units to common stock	0	3,000	6,717,000	0	0	0	(6,720,000)	0	0
Issuance of common stock through exercise of options	3,856,000	1,000	3,855,000	0	0	0	0	0	0
Issuance of common stock through employee stock purchase plan	1,076,000	0	1,076,000	0	0	0	0	0	0
Compensation expenses related to stock options and restricted stock	5,797,000	0	5,797,000	0	0	0	0	0	0
Repurchase of common stock or Common OP Units	(1,287,000)	0	(1,287,000)	0	0	0	0	0	0
Adjustment for Common OP Unitholders in the Operating Partnership	0	0	(450,000)	0	0	0	450,000	0	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(43,000)	0	0	0	0	0	0	0	43,000
Net income	54,778,000
Distributions	(79,105,000)	0	0	0	0	(72,409,000)	(6,696,000)	0	0
Net Income (Loss) Attributable to Parent	59,845,000	0	0	0	0	54,778,000	5,067,000	0	0
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	(504,000)	0	(504,000)	0	0	0	0	0	0
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs, Preferred Stock Offering Costs	(757,000)	0	(757,000)	0	0	0	0	0	0
Temporary Equity Conversion To Permanent Equity	200,000,000	0	0	200,000,000	0	0	0	0	0
Stock Exchange	0	0	0	(136,144,000)	136,144,000	0	0	0	0
Payments for Repurchase of Preferred Stock and Preference Stock	(63,856,000)	0	0	(63,856,000)	0	0	0	0	0
Ending Balance at Dec. 31, 2012	$ 924,302,000	$ 416,000	$ 1,012,930,000	$ 0	$ 136,144,000	$ (287,652,000)	$ 65,054,000	$ 0	$ (2,590,000)