Schedule III - Real Estate And Accumulated Depreciation (Changes in Real Estate and Accumulated Depreciation)(Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in real estate
Balance at beginning of year	$ 7,203,216	$ 6,670,210	$ 6,289,687
Acquisitions	329,996	491,023	479,236
Improvements	93,439	102,530	110,054
Retirements/disposals	(198,408)	(60,547)	(208,767)
Balance at end of year	7,428,243	7,203,216	6,670,210
Aggregate cost of land, buildings and improvements, before depreciation, for Federal income tax purposes	5,100,000
Changes in accumulated depreciation, exclusive of amounts relating to equipment, autos, and furniture and fixtures
Balance at beginning of year	1,123,412	983,273	848,077
Depreciation for year	175,039	165,840	160,539
Retirements/disposals	(30,853)	(25,701)	(25,343)
Balance at end of year	$ 1,267,598	$ 1,123,412	$ 983,273