Schedule III - Real Estate and Accumulated Depreciation (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Accumulated depreciation, beginning of year	$ 994,241	$ 947,664	$ 818,957
Depreciation of real estate	171,983	159,524	153,841
SEC Schedule III, Real Estate Accumulated Depreciation, Period Increase	171,983	159,524	153,841
Write-offs due to sale	(22,471)	(66,603)	(18,111)
Properties held for sale	(3,900)	(46,191)	(7,007)
Other additions	0
Other deductions		(153)	(16)
Total deductions during period	(26,371)	(112,947)	(25,134)
Accumulated depreciation, end of year	$ 1,139,853	$ 994,241	$ 947,664