Stockholders’ Equity and Earnings (Loss) per Share - Basic and Diluted Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net loss (numerator):
Net loss	$ (3,937)	$ (5,980)	$ (11,396)	$ (18,553)
Loss per share:
Basic and diluted (in dollars per share)	$ (0.10)	$ (0.16)	$ (0.30)	$ (0.49)
Shares (denominator):
Weighted average common shares outstanding - basic (in shares)	38,253	37,839	38,210	37,688
Weighted average common shares outstanding - diluted (in shares)	38,253	37,839	38,210	37,688