Investments in Unconsolidated Joint Ventures (Details 3) (USD $)	3 Months Ended		6 Months Ended			12 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2012 717 Fifth Avenue	Jun. 30, 2013 Joint venture	Jun. 30, 2012 Joint venture	Jun. 30, 2013 Joint venture	Jun. 30, 2012 Joint venture	Dec. 31, 2012 Joint venture
Assets
Commercial real estate property, net	$ 10,160,569,000		$ 10,160,569,000		$ 10,269,630,000		$ 6,727,061,000		$ 6,727,061,000		$ 6,910,991,000
Other assets	699,256,000		699,256,000		718,326,000		853,956,000		853,956,000		728,113,000
Total assets							7,581,017,000		7,581,017,000		7,639,104,000
Liabilities and members' equity
Mortgages and other loan payable	4,835,231,000		4,835,231,000		4,615,464,000		5,195,209,000		5,195,209,000		5,358,048,000
Other liabilities							377,491,000		377,491,000		406,929,000
Members' equity							2,008,317,000		2,008,317,000		1,874,127,000
Total liabilities and members' equity							7,581,017,000		7,581,017,000		7,639,104,000
Company's net investment in unconsolidated joint ventures	1,085,793,000		1,085,793,000		1,032,243,000		1,085,793,000		1,085,793,000		1,032,243,000
Combined statements of income for the unconsolidated joint ventures
Total revenues		244,466,000					154,974,000	124,418,000	306,205,000	244,466,000
Operating expenses	69,432,000	67,434,000	141,630,000	139,319,000			28,205,000	16,207,000	56,816,000	32,973,000
Ground rent	8,649,000	8,890,000	19,640,000	17,696,000			658,000	742,000	1,315,000	1,660,000
Real estate taxes	52,710,000	52,256,000	106,114,000	103,453,000			16,958,000	12,483,000	34,263,000	25,857,000
Interest expense, net of interest income	83,276,000	82,159,000	164,447,000	162,130,000			56,561,000	50,602,000	112,968,000	105,470,000
Amortization of deferred financing costs	4,240,000	3,553,000	8,703,000	7,133,000			5,302,000	2,904,000	9,585,000	4,671,000
Depreciation and amortization	82,020,000	76,207,000	161,114,000	151,739,000			52,539,000	35,724,000	95,150,000	72,507,000
Transaction related costs	1,711,000	1,970,000	3,068,000	3,026,000				90,000		358,000
Total expenses	323,552,000	313,190,000	647,298,000	625,977,000			160,223,000	118,752,000	310,097,000	243,496,000
Net (loss) income							(5,249,000)	5,666,000	(3,892,000)	970,000
Company's equity in net (loss) income of unconsolidated joint ventures	(3,761,000)	70,890,000	1,313,000	69,330,000			(3,761,000)	70,890,000	1,313,000	69,330,000
Additional cash income recognized due to distribution of refinancing proceeds						$ 67,900,000