Stock Purchase Warrants (Details) $ in Thousands			12 Months Ended
	Dec. 27, 2017 shares	Dec. 21, 2017 USD ($) shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 06, 2017 $ / shares
Stock Purchase Warrants
Proceeds from issuance of warrants | $			$ 0	$ 207	$ 190
ICT
Stock Purchase Warrants
License Agreement, Initial Payment | $		$ 5,200
Common Stock
Stock Purchase Warrants
Exercise of warrants resulting in the issuance of common stock (in shares)			681,000	817,000
Conversion of preferred stock for common stock (Note 9) (in shares)				1,094,000
December 2017 Warrants
Stock Purchase Warrants
Exercise price (in dollars per share) | $ / shares			$ 4.27
Total shares issuable on exercise			26,951
Expected life (years)						6 years
December 2017 Warrants | Common Stock
Stock Purchase Warrants
Conversion of preferred stock for common stock (Note 9) (in shares)			19,750
December 2017 Warrants | Closing stock price
Stock Purchase Warrants
Warrants and Rights Outstanding | $ / shares						5.10
December 2017 Warrants | Expected dividend yield
Stock Purchase Warrants
Warrants and Rights Outstanding						0.00
December 2017 Warrants | Expected stock price volatility
Stock Purchase Warrants
Warrants and Rights Outstanding						0.864
December 2017 Warrants | Risk-free interest rate
Stock Purchase Warrants
Warrants and Rights Outstanding						0.022
August 2013 Warrants
Stock Purchase Warrants
Exercise price (in dollars per share) | $ / shares			$ 4.8
August 2013 Warrants | Common Stock
Stock Purchase Warrants
Conversion of preferred stock for common stock (Note 9) (in shares)			565,895
September 2016 Warrants
Stock Purchase Warrants
Exercise price (in dollars per share) | $ / shares			$ 2.25
Total shares issuable on exercise			117,074
September 2016 Warrants | Common Stock
Stock Purchase Warrants
Conversion of preferred stock for common stock (Note 9) (in shares)			95,335
December 21, 2017 Warrants | ICT
Stock Purchase Warrants
Exercise price (in dollars per share) | $ / shares						$ 0.01
Total shares issuable on exercise		818,424
Proceeds from issuance of warrants | $		$ 4,000
Share Price | $ / shares						$ 4.90
Exercise of warrants resulting in the issuance of common stock (in shares)	816,850
Warrants outstanding (in shares)				0
Potential Payment
Stock Purchase Warrants
Other Commitment | $			$ 1,300	$ 1,200
Potential Payment | ICT
Stock Purchase Warrants
Other Commitment | $		$ 1,200