Schedule III Part II - Summary of Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate and Accumulated Depreciation, Carrying Amount of Land and Buildings and Improvements [Abstract]
Balance at beginning of year	$ 6,759,073	$ 6,064,406	$ 5,608,998
Acquisitions	555,476	229,296	291,726
Improvements	492,541	483,932	281,471
Deduction during period—dispositions and retirements of property	172,029	18,561	117,789
Balance at end of year	7,635,061	6,759,073	6,064,406
Aggregate cost basis for Federal tax purposes	6,700,000
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at beginning of year	1,729,234	1,574,041	1,467,050
Additions during period—depreciation and amortization expense	193,340	173,244	156,513
Deductions during period—dispositions and retirements of property	46,030	18,051	49,522
Balance at end of year	$ 1,876,544	$ 1,729,234	$ 1,574,041