Deferred Charges and Other Assets, net: (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Leasing	$ 239,955	$ 223,038
Financing	47,171	51,695
Intangible assets:
In-place lease values	298,825	205,651
Leasing commissions and legal costs	72,432	50,594
Above-market leases	250,810	118,770
Deferred tax assets	35,625	31,356
Deferred compensation plan assets	35,194	30,932
Other assets	66,246	65,793
Deferred charges and other assets, gross	1,046,258	777,829
Less accumulated amortization	(287,197)	(244,771)
Deferred charges and other assets, net	759,061	533,058
Accumulated amortization for in-place lease values, leasing commissions and legal costs	103,361	89,141
Amortization expense for intangible assets	$ 52,668	$ 53,139	$ 32,456