CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets
Accounts receivable allowance	$ 1,557	$ 1,186
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	160,000,000	160,000,000
Common stock, shares issued	54,099,927	53,003,420
Common stock, shares outstanding	54,080,192	52,983,685