Offering Costs and Formation Transaction Expenses - Schedule of Correction of Immaterial Error on Combined Financial Statements (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended			6 Months Ended		3 Months Ended	9 Months Ended	6 Months Ended		3 Months Ended	9 Months Ended	6 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2012	Dec. 31, 2010	Jun. 30, 2012 As reported	Dec. 31, 2011 As reported	Sep. 30, 2011 As reported 250 West 57th ST. Associates L.L.C.	Sep. 30, 2011 As reported 250 West 57th ST. Associates L.L.C.	Jun. 30, 2012 Adjustment	Dec. 31, 2011 Adjustment	Sep. 30, 2011 Adjustment 250 West 57th ST. Associates L.L.C.	Sep. 30, 2011 Adjustment 250 West 57th ST. Associates L.L.C.	Jun. 30, 2012 As adjusted	Dec. 31, 2011 As adjusted	Sep. 30, 2011 As adjusted 250 West 57th ST. Associates L.L.C.	Sep. 30, 2011 As adjusted 250 West 57th ST. Associates L.L.C.
Organization And Offering Costs [Line Items]
Deferred costs, net	$ 1,414,890		$ 1,414,890		$ 790,019	$ 252,337			$ 1,003,519				$ (213,500)				$ 790,019
Members' deficiency	(2,698,822)		(2,698,822)		(4,855,980)		(4,860,381)		(4,642,480)				(213,500)				(4,855,980)
Formation transaction expenses	56,738	41,589	95,575	81,417								38,837		41,589	81,417	38,837		41,589	81,417
Net income	3,124,130	3,858,372	2,697,158	3,580,877	3,287,105			(388,135)		3,899,961	3,662,294	(38,837)		(41,589)	(81,417)	(426,972)		3,858,372	3,580,877
Net cash provided by operating activities			782,403	673,290				577,173			754,707	(38,837)			(81,417)	538,336			673,290
Net cash used in financing activities			(1,855,027)	(1,566,935)				(1,286,315)			(1,648,352)	38,837			81,417	(1,247,478)			(1,566,935)
Net change in cash and cash equivalents			$ (1,055,640)	$ (733,696)				$ (692,158)			$ (733,696)					$ (692,158)			$ (733,696)