Schedule III - Real Estate and Accumulated Depreciation (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Beginning Balance, Total Property	$ 3,382,680	$ 3,271,536	$ 3,084,166
Retirement/dispositions:
Ending Balance, Total Property	3,633,993	3,382,680	3,271,536
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Beginning Balance, Accumulated Depreciation	762,996	705,135	642,320
Retirement/dispositions:
Ending Balance, Accumulated Depreciation	843,816	762,996	705,135
Real Estate [Member]
Additions during the period:
Total Property	239,265	183,478	166,290
Retirement/dispositions:
Total Property	(94,143)	(139,741)	(74,507)
Ending Balance, Total Property	3,596,632
Additions during the period:
Accumulated Depreciation	3,898	3,048	2,272
Retirement/dispositions:
Accumulated Depreciation	(44,696)	(56,838)	(46,276)
Ending Balance, Accumulated Depreciation	839,483
Other improvements [Member]
Additions during the period:
Total Property	70,595	47,985	55,340
Additions during the period:
Accumulated Depreciation	121,592	111,625	105,257
Corporate Property [Member]
Additions during the period:
Total Property	0	0	40,247
Retirement/dispositions:
Ending Balance, Total Property	5,583
Additions during the period:
Accumulated Depreciation	0	0	1,536
Retirement/dispositions:
Ending Balance, Accumulated Depreciation	4,167
Land held for development [Member]
Additions during the period:
Total Property	0	500	0
Retirement/dispositions:
Total Property	0	(102)	0
Additions during the period:
Accumulated Depreciation	26	26	26
Retirement/dispositions:
Accumulated Depreciation	0	0	0
Construction in Progress [Member]
Additions during the period:
Total Property	35,596	19,024	0
Retirement/dispositions:
Ending Balance, Total Property	11,655
Additions during the period:
Accumulated Depreciation	0	0	0
Disposal of previously consolidated VIE [Member]
Retirement/dispositions:
Total Property	0	0	0
Retirement/dispositions:
Accumulated Depreciation	$ 0	$ 0	$ 0