Segment Information (Summary of NOI by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Property-level revenues	$ 536,226	$ 528,755	$ 511,087	$ 508,058	$ 513,974	$ 502,753	$ 498,098	$ 488,917	$ 2,084,126	$ 2,003,742	$ 1,985,495
Property-level expenses									886,596	844,566	824,511
NOI - consolidated									1,197,530	1,159,176	1,160,984
Deduct: NOI attributable to noncontrolling interests in consolidated subsidiaries									(65,311)	(66,182)	(64,859)
Add: Our share of NOI from partially owned entities									269,164	271,114	245,750
NOI at share									1,401,383	1,364,108	1,341,875
Non-cash adjustments for straight-line rents, amortization of acquired below-market leases, net and other									(86,842)	(170,477)	(214,322)
NOI at share - cash basis									1,314,541	1,193,631	1,127,553
Balance Sheet Data:
Real estate, at cost	14,756,295				14,187,820				14,756,295	14,187,820	13,545,295	$ 12,438,940
Investments in partially owned entities	1,056,829				1,378,254				1,056,829	1,378,254
Assets	17,397,934				20,814,847				17,397,934	20,814,847
New York
Segment Reporting Information [Line Items]
Property-level revenues									1,779,307	1,713,374	1,695,925
Property-level expenses									756,670	716,754	694,228
NOI - consolidated									1,022,637	996,620	1,001,697
Deduct: NOI attributable to noncontrolling interests in consolidated subsidiaries									(45,899)	(47,480)	(42,905)
Add: Our share of NOI from partially owned entities									189,327	159,386	156,177
NOI at share									1,166,065	1,108,526	1,114,969
Non-cash adjustments for straight-line rents, amortization of acquired below-market leases, net and other									(79,202)	(143,239)	(186,781)
NOI at share - cash basis									1,086,863	965,287	928,188
Balance Sheet Data:
Real estate, at cost	11,025,092				10,787,730				11,025,092	10,787,730
Investments in partially owned entities	861,430				1,026,793				861,430	1,026,793
Assets	13,780,817				13,310,524				13,780,817	13,310,524
Other
Segment Reporting Information [Line Items]
Property-level revenues									304,819	290,368	289,570
Property-level expenses									129,926	127,812	130,283
NOI - consolidated									174,893	162,556	159,287
Deduct: NOI attributable to noncontrolling interests in consolidated subsidiaries									(19,412)	(18,702)	(21,954)
Add: Our share of NOI from partially owned entities									79,837	111,728	89,573
NOI at share									235,318	255,582	226,906
Non-cash adjustments for straight-line rents, amortization of acquired below-market leases, net and other									(7,640)	(27,238)	(27,541)
NOI at share - cash basis									227,678	228,344	$ 199,365
Balance Sheet Data:
Real estate, at cost	3,731,203				3,400,090				3,731,203	3,400,090
Investments in partially owned entities	195,399				351,461				195,399	351,461
Assets	$ 3,617,117				$ 7,504,323				$ 3,617,117	$ 7,504,323