Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Consolidated Balance Sheets
Allowances on accounts receivable	$ 2,000	$ 1,890
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	50,000	50,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	750,000	750,000
Common stock, shares issued	54,040	52,665
Common stock, shares outstanding	54,040	52,665