Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements of Stockholder's Equity
Cash dividends declared on common stock, per share	$ 0.50	$ 0.40	$ 0.40
Common stock issued, per share	$ 30.91	$ 26.42	$ 27.76