Deferred Charges and Other Assets, net: (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Leasing	$ 246,144		$ 246,144		$ 239,955
Financing	49,020		49,020		47,171
Intangible assets:
In-place lease values	274,407		274,407		298,825
Leasing commissions and legal costs	69,680		69,680		72,432
Above-market leases	257,869		257,869		250,810
Deferred tax assets	37,727		37,727		35,625
Deferred compensation plan assets	35,419		35,419		35,194
Other assets	93,405		93,405		66,246
Deferred charges and other assets, gross	1,063,671		1,063,671		1,046,258
Less accumulated amortization	(329,298)		(329,298)		(287,197)
Deferred charges and other assets, net	734,373		734,373		759,061
Accumulated amortization for intangible assets	120,754		120,754		$ 103,361
Amortization expense for intangible assets	$ 16,864	$ 11,850	$ 57,208	$ 35,948