Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,181,000	$ 0
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
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)	150,000,000	150,000,000
Common stock, shares issued (in shares)	60,608,000	59,596,000
Common stock, shares outstanding (in shares)	49,103,000	48,854,000
Treasury stock, shares (in shares)	11,505,000	10,742,000