Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Stockholders' equity:
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	15,000,000.0	15,000,000.0
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000.0	200,000,000.0
Common stock, shares issued (in shares)	52,700,000	52,400,000
Common stock, shares outstanding (in shares)	51,600,000	51,200,000
Treasury stock (in shares)	1,200,000	1,200,000