Investment in Unconsolidated Joint Ventures Investment in Unconsolidated Joint Ventures-Additional Information (Details) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			1 Months Ended	0 Months Ended				1 Months Ended		1 Months Ended
	Sep. 30, 2014 sqft	Sep. 30, 2013	Sep. 30, 2014 sqft	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Joint Venture	Sep. 30, 2013 Joint Venture	Sep. 30, 2014 Joint Venture	Sep. 30, 2013 Joint Venture	Dec. 31, 2013 Joint Venture	Sep. 30, 2014 180 Broadway	May 31, 2014 747 Madison Avenue	May 31, 2014 747 Madison Avenue unit	Sep. 30, 2014 747 Madison Avenue Joint Venture	May 31, 2014 747 Madison Avenue Joint Venture	Mar. 31, 2014 West Coast office portfolio	Mar. 31, 2014 West Coast office portfolio Joint Venture	Jan. 31, 2014 21 West 34th Street sqft	Jan. 31, 2014 21 West 34th Street Joint Venture	Mar. 31, 2014 Participating Financing Due March 2016
Investment in Unconsolidated Joint Ventures
Net equity investment in VIEs in which the entity is not primary beneficiary	$ 174,400,000		$ 174,400,000		$ 310,700,000
Real Estate fair value											222,500,000		160,000,000			756,000,000		114,900,000
Promote income											3,300,000	10,300,000
Deferred gain on sale											16,500,000	13,100,000
Joint venture ownership percentage sold (percent)												33.33%				43.74%		49.90%
Ownership Interest (as a percent)														100.00%
Number of units in property (units)													5
Total floating rate debt	1,606,152,000		1,606,152,000		729,949,000	1,604,619,000		1,604,619,000		1,842,815,000					33,100,000		526,300,000		100,000,000
Preferred equity investment													30,000,000
Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate	16,496,000	(354,000)	122,580,000	(3,937,000)												85,500,000		20,900,000
Acquisition origination financing																				100,000,000
Loans and leases receivables																				60,000,000
Debt and preferred equity investments	1,432,951,000		1,432,951,000		1,304,839,000															40,000,000
Area of property (sqft)	33,892,903		33,892,903															91,300
Management fees, base revenue						$ 3,800,000	$ 3,500,000	$ 15,000,000	$ 7,500,000