Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Condensed Consolidated Balance Sheets
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, shares issued (in shares)	40,039,172	39,024,337
Common stock, shares outstanding (in shares)	30,922,653	30,825,123
Treasury stock, shares (in shares)	9,116,519	8,199,214