Subsequent Events (Narratives) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Oct. 01, 2013 Subsequent Event [Member] New York Harlem Park 1800 Park Avenue [Member] Other Segment [Member]	Oct. 04, 2013 Subsequent Event [Member] New York 655 Fifth Avenue [Member] New York Segment [Member] sqft ft	Oct. 15, 2013 Subsequent Event [Member] New York Manhattan 220 Central Park South Site [Member] Other Segment [Member] sqft
Subsequent Event [Line Items]
Gross proceeds from sale of real estate					$ 66,000
Net proceeds from sale of real estate					63,000
Net gain on sale of of real estate	18,996	131,088	286,990	203,801	23,000
Business acquisition description of acquisition						On October 4, 2013, we acquired a 92.5% interest in 655 Fifth Avenue, a 57,500 square foot retail and office property located at the northeast corner of Fifth Avenue and 52nd Street in Manhattan with 50 feet of frontage on Fifth Avenue, for $277,500,000 in cash. We consolidate the accounts of the property into our consolidated financial statements.	On October 15, 2013, we acquired, for $194,000,000, land and air rights for 137,000 zoning square feet thereby completing the assemblage for our 220 Central Park South site in Manhattan.
Equity method ownership percentage						92.50%
Square Footage Of Real Estate Property						57,500	137,000
Frontage Length						50
Cost Of Acquired Entity Purchase Price						$ 277,500	$ 194,000