Equity (Details 2) (USD $)	9 Months Ended			0 Months Ended	9 Months Ended	1 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Minimum Lehman Brothers Holdings, Inc	Feb. 27, 2013 Archstone	Sep. 30, 2013 Archstone	May 31, 2013 Archstone Lehman Brothers Holdings, Inc	Aug. 31, 2012 CEP III	Sep. 30, 2013 CEP III
Equity
Common stock shares issued in connection with stock options exercised	33,900
Common stock shares issued through dividend reinvestment plan	1,465	1,830
Common stock shares issued in connection with stock grants	123,977	96,592
Number of shares of stock grants withheld	44,750	120,952
Restricted common stock shares forfeited	5,214
Number of shares issued				14,889,706	14,889,706
Ownership percentage of common stock considered as restriction to acquire additional forms of ownership			5.00%
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
Value of additional shares authorized for issuance								$ 646,274,000
Common stock shares issued								0