Net Gain on Disposition of Full or Partial Interest in Rental Properties (Details) (USD $)	11 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Jan. 31, 2013	Jan. 31, 2012
Significant Acquisitions and Disposals [Line Items]
Net gain on disposition of full or partial interest in rental properties	$ 496,092,000	$ 0	$ 30,281,000	$ 0
Forest Trace [Member]
Significant Acquisitions and Disposals [Line Items]
Net gain on disposition of full or partial interest in rental properties	0		23,013,000	0
Halle Building [Member]
Significant Acquisitions and Disposals [Line Items]
Net gain on disposition of full or partial interest in rental properties	0		7,881,000	0
Stapleton-3055 Roslyn [Member]
Significant Acquisitions and Disposals [Line Items]
Net gain on disposition of full or partial interest in rental properties	0		(146,000)	0
QIC Joint Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Net gain on disposition of full or partial interest in rental properties	381,627,000		(467,000)	0
New York Retail Joint Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Net gain on disposition of full or partial interest in rental properties	$ 114,465,000		$ 0	$ 0	$ 9,561,000