Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders’ equity:
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.004	$ 0.004	$ 0.004
Common stock, shares authorized (in shares)	100,000,000	100,000,000	100,000,000
Common stock, shares issued (in shares)	52,078,515	51,991,242	52,422,801
Common stock, shares outstanding (in shares)	52,078,515	51,991,242	52,422,801