CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Stockholders' equity:
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)	45,124,948	43,174,676
Common stock, shares outstanding (in shares)	34,394,412	32,854,802
Treasury stock, shares (in shares)	10,730,536	10,319,874