Consolidated Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
Investment in real estate:
Land	$ 1,025,246,000	$ 984,224,000
Land Improvements	2,667,213,000	2,565,299,000
Buildings and other depreciable property	535,647,000	495,127,000
Real Estate Investment Property, at Cost	4,228,106,000	4,044,650,000
Accumulated depreciation	(1,058,540,000)	(948,581,000)
Net investment in real estate	3,169,566,000	3,096,069,000
Cash	58,427,000	37,126,000
Notes receivable, net	42,990,000	45,469,000
Investment in joint ventures	11,583,000	8,420,000
Deferred financing costs, net	19,873,000	20,620,000
Deferred commission expense	25,251,000	22,841,000
Escrow deposits and other assets	63,949,000	47,829,000
Total Assets	3,391,639,000	3,398,226,000
Assets of Disposal Group, Including Discontinued Operation	0	119,852,000
Liabilities:
Mortgage notes payable	1,992,368,000	2,061,610,000
Term loan	200,000,000	200,000,000
Unsecured lines of credit	0	0
Accrued payroll and other operating expenses	65,157,000	63,672,000
Deferred revenue-upfront payments from right-to-use contracts	68,673,000	62,979,000
Deferred revenue-right-to-use annual payments	11,136,000	11,088,000
Accrued interest payable	9,416,000	10,500,000
Rents and other customer payments received in advance and security deposits	58,931,000	54,017,000
Distributions payable	22,753,000	0
Total Liabilities	2,428,434,000	2,473,924,000
Liabilities of Disposal Group, Including Discontinued Operation	0	10,058,000
Stockholders' Equity:
Preferred stock, $.01 par value 2,000,000 shares authorized; none issued and outstanding as of December 31, 2011 and 2010	0	0
Common stock, $.01 par value 100,000,000 shares authorized for 2011 and 2010; 41,078,200 and 30,972,353 shares issued and outstanding for 2011 and 2010, respectively	834,000	832,000
Paid-in capital	1,021,365,000	1,012,514,000
Distributions in excess of accumulated earnings	264,083,000	287,652,000
Accumulated other comprehensive loss	(927,000)	(2,590,000)
Total Stockholders' Equity	893,333,000	859,248,000
Non-controlling interests-Common OP Units	69,872,000	65,054,000
Total Equity	963,205,000	924,302,000
Total Liabilities and Equity	3,391,639,000	3,398,226,000
Cumulative Series C Six Point Seven Five Percent Redeemable Perpetual Preferred Stock [Domain]
Stockholders' Equity:
Preferred stock, $.01 par value 2,000,000 shares authorized; none issued and outstanding as of December 31, 2011 and 2010	$ 136,144,000	$ 136,144,000