Schedule III - Real Estate and Accumulated Depreciation (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Beginning Balance, Total Property	$ 3,907,010	$ 3,633,993	$ 3,382,680
Retirement/dispositions:
Ending Balance, Total Property	3,993,427	3,907,010	3,633,993
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Beginning Balance, Accumulated Depreciation	933,220	843,816	762,996
Retirement/dispositions:
Ending Balance, Accumulated Depreciation	1,025,831	933,220	843,816
Real Estate [Member]
Additions during the period:
Total Property	112,591	322,616	239,265
Retirement/dispositions:
Total Property	(132,665)	(123,639)	(94,143)
Ending Balance, Total Property	3,930,173
Additions during the period:
Accumulated Depreciation	4,175	4,206	3,898
Retirement/dispositions:
Accumulated Depreciation	(69,102)	(50,683)	(44,696)
Ending Balance, Accumulated Depreciation	1,020,971
Other improvements [Member]
Additions during the period:
Total Property	74,317	59,442	70,595
Additions during the period:
Accumulated Depreciation	157,385	135,807	121,592
Land held for development [Member]
Additions during the period:
Total Property	4,525	0	0
Retirement/dispositions:
Total Property	0	0	0
Additions during the period:
Accumulated Depreciation	153	74	26
Retirement/dispositions:
Accumulated Depreciation	0	0	0
Construction in Progress [Member]
Additions during the period:
Total Property	27,649	14,598	35,596
Retirement/dispositions:
Ending Balance, Total Property	33,107
Additions during the period:
Accumulated Depreciation	$ 0	$ 0	$ 0