Equity (Details 2) (USD $)	6 Months Ended			0 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Minimum Lehman Brothers Holdings, Inc	Feb. 27, 2013 Archstone	Jun. 30, 2013 Archstone	May 31, 2013 Archstone Lehman Brothers Holdings, Inc	Jun. 30, 2013 Archstone Lehman Brothers Holdings, Inc	Aug. 31, 2012 CEP III	Jun. 30, 2013 CEP III
Equity
Common stock shares issued in connection with stock options exercised	30,118
Common stock shares issued through dividend reinvestment plan	1,030	1,336
Common stock shares issued in connection with stock grants	123,977	95,941
Number of shares of stock grants withheld	44,222	120,078
Restricted common stock shares forfeited	5,214
Number of shares issued				14,889,706	14,889,706		14,889,706
Ownership percentage of common stock considered as restriction to acquire additional forms of ownership			5.00%
Value of shares sold by Lehman						$ 7,870,000
Options of common stock granted to employees (in shares)	215,230
Maximum value of shares of common stock that can be sold (in dollars)								$ 750,000,000
Period during which common stock can be sold								36 months
Additional shares authorized for issuance									646,274,000
Common stock shares issued									0