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 Subordinated Non-Voting Cumulative Redeemable Preferred Stock	Accumulated Other Comprehensive Income
Beginning Balance at Dec. 31, 2010	$ 260,158,000	$ 726,000	$ 463,306,000	$ 0	$ 0	$ (237,002,000)	$ 33,128,000	$ 0	$ 0
Payments for Repurchase of Preferred Stock and Preference Stock	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
Ending Balance at Dec. 31, 2011	799,280,000	828,000	998,067,000	0	0	(270,021,000)	72,953,000	0	(2,547,000)
Payments for Repurchase of Preferred Stock and Preference Stock	(63,856,000)	0	0	(63,856,000)	0	0	0	0	0
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
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
Net income	54,779,000
Distributions	(79,106,000)	0	0	0	0	(72,410,000)	(6,696,000)	0	0
Stock Exchange	0	0	0	(136,144,000)	136,144,000	0	0	0	0
Net Income (Loss) Attributable to Parent	59,846,000	0	0	0	0	54,779,000	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
Temporary Equity Conversion To Permanent Equity	200,000,000	0	0	200,000,000	0	0	0	0	0
Ending Balance at Dec. 31, 2012	924,302,000	832,000	1,012,514,000	0	136,144,000	(287,652,000)	65,054,000	0	(2,590,000)
Payments for Repurchase of Preferred Stock and Preference Stock	0
Conversion of OP Units to common stock	0	0	280,000	0	0	0	(280,000)	0	0
Issuance of common stock through exercise of options	248,000	1,000	247,000	0	0	0	0	0	0
Issuance of common stock through employee stock purchase plan	720,000	1,000	719,000	0	0	0	0	0	0
Compensation expenses related to stock options and restricted stock	5,952,000	0	5,952,000	0	0	0	0	0	0
Repurchase of common stock or Common OP Units	(1,121,000)	0	(1,121,000)	0	0	0	0	0	0
Adjustment for Common OP Unitholders in the Operating Partnership	0	0	(6,730,000)	0	0	0	6,730,000	0	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(1,663,000)	0	0	0	0	0	0	0	(1,663,000)
Net income	106,919,000
Distributions	(100,194,000)	0	0	0	(9,280,000)	(83,350,000)	(7,564,000)	0	0
Net Income (Loss) Attributable to Parent	125,905,000	0	0	0	9,280,000	106,919,000	9,706,000	0	0
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	544,000	0	544,000	0	0	0	0	0	0
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs, Preferred Stock Offering Costs	(3,412,000)	0	3,412,000	0	0	0	0	0	0
Stock Exchange	9,686,000	0	0	0	0	0	9,686,000	0	0
Ending Balance at Dec. 31, 2013	$ 963,205,000	$ 834,000	$ 1,021,365,000	$ 0	$ 136,144,000	$ (264,083,000)	$ 69,872,000	$ 0	$ (927,000)