Subsequent Events (Details) (USD $)	3 Months Ended			12 Months Ended			1 Months Ended		1 Months Ended
	Dec. 31, 2012	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 31, 2013 Mezzanine loan	Feb. 28, 2013 Subsequent event 1515 Broadway	Jan. 31, 2013 Subsequent event Mezzanine loan	Feb. 28, 2013 Subsequent event Refinancing of Debt 1515 Broadway
Subsequent Events
Percentage of loan sold							50.00%		50.00%
Face amount of loan sold								$ 775,000,000	$ 118,200,000
Consideration from sale of loan									57,800,000
Additional income generated	(6,978,000)	(67,000)	971,000	(6,978,000)	904,000	(1,900,000)			12,900,000
Refinanced mortgage loan										$ 900,000,000
Term of refinanced mortgage										12 years
Interest rate (as a percent)										3.93%