Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,183	$ 1,069
Unamortized discount, current	835	699
Unamortized discount, noncurrent	$ 2,055	$ 1,969
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, shares issued (in shares)	21,516,738	20,768,401
Common stock, shares outstanding (in shares)	21,516,738	20,768,401