CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Dec. 31, 2011	Dec. 31, 2010
CONSOLIDATED BALANCE SHEETS
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	61,854,474	60,208,506
Common stock, shares outstanding	47,748,699	46,901,511
Treasury shares	14,105,775	13,306,995