Schedule III Part II - Summary of Real Estate and Accumulated Depreciation (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Real Estate and Accumulated Depreciation, Carrying Amount of Land and Buildings and Improvements [Abstract]
Balance at beginning of year	$ 4,779,674,000	$ 4,426,444,000	$ 3,895,942,000
Acquisitions	76,359,000	193,131,000	430,758,000
Improvements	329,522,000	187,990,000	147,996,000
Real Estate Deconsolidation of VIE			(18,311,000)
Deduction during period - disposition and retirements of property	(36,092,000)	(27,891,000)	(29,941,000)
Balance at end of year	5,149,463,000	4,779,674,000	4,426,444,000
Real Estate and Accumulated Depreciation, Other Required Disclosures [Abstract]
Real Estate, Federal Income Tax Basis	4,500,000,000
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at beginning of year	1,224,295,000	1,127,588,000	1,035,204,000
Additions during period—depreciation and amortization expense	147,730,000	128,654,000	114,180,000
Deductions during period—disposition and retirements of property	(21,554,000)	(31,947,000)	(21,796,000)
Balance at end of year	$ 1,350,471,000	$ 1,224,295,000	$ 1,127,588,000