Consolidated Statements of Equity (Parenthetical) (USD $)	3 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements of Equity
Cash distribution declared, per common share (in dollars per share)	$ 0.33	$ 0.25	$ 0.10	$ 1.08	$ 0.55	$ 0.40