Segment Information (Other EBITDA components) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Information
General and administrative	$ (179,279)	$ (175,307)	$ (169,270)
Acquisition and transaction related costs	(26,037)	(12,511)	(18,435)
Gain (Loss) from disposal of real estate	5,074	65,396	507,192
Non cash impairment losses	20,290	21,260	85,459
EBITDA	2,173,985	1,852,766	2,277,084
Mark-to-market of investments in our deferred compensation plan	$ 5,213	111	11,557
Real estate fund investments
Segment Information
Equity method ownership percentage	25.00%
Operating Segments | Other
Segment Information
Our share of Net (Loss) Income	$ 199,555	211,967	330,237
General and administrative	(100,594)	(106,416)	(94,929)
Investment Income Net	22,501	26,385	31,665
Acquisition and transaction related costs	(26,062)	(12,511)	(16,392)
Gain (Loss) from disposal of real estate	7,185	28,314	245,679
Net gain on sale of real estate	714	44,390	26,568
EBITDA	250,180	175,772	506,794
Mark-to-market of investments in our deferred compensation plan	5,213	111	11,557
Operating Segments | Other | 2012-2014 Out Performance Plans
Segment Information
Additional Expense From Acceleration Of Vesting		4,542
Operating Segments | Other | The Mart and trade shows
Segment Information
Our share of Net (Loss) Income	91,845	79,159	79,636
Operating Segments | Other | 555 California Street
Segment Information
Our share of Net (Loss) Income	45,827	49,975	48,844
Operating Segments | Other | India real estate ventures
Segment Information
Our share of Net (Loss) Income	3,685	3,933	6,434
Impairment Of Real Estate	(13,962)	(14,806)	(5,771)
Operating Segments | Other | 85 Tenth Avenue
Segment Information
Income from repayment of Investment in real estate	160,843	0	0
Operating Segments | Other | Our share of Toys "R" Us
Segment Information
Our share of Net (Loss) Income	2,000	2,500	103,632
Non cash impairment losses			75,196
Operating Segments | Other | Suffolk Downs
Segment Information
Non cash impairment losses	0	(1,551)	(10,263)
Operating Segments | Other | Other investment
Segment Information
Our share of Net (Loss) Income	$ 77,240	42,436	21,385
Operating Segments | Other | Fashion Centre Mall / Washington Tower
Segment Information
Equity method ownership percentage	7.50%
Real estate disposition transaction cost		14,956	22,684
Operating Segments | Other | Real estate fund investments
Segment Information
Our share of Net (Loss) Income	$ (21,042)	33,964	70,306
Operating Segments | Other | Real estate fund investments | Income before net realized/unrealized gains
Segment Information
Our share of Net (Loss) Income	8,607	8,611	8,056
Operating Segments | Other | Real estate fund investments | Net unrealized/realized gains on investments
Segment Information
Our share of Net (Loss) Income	(16,270)	14,657	37,535
Operating Segments | Other | Real estate fund investments | Carried Interest
Segment Information
Our share of Net (Loss) Income	$ (13,379)	$ 10,696	$ 24,715