Stockholders' Equity - Estimates Utilized (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity Note [Abstract]
Fair value of options issued (in dollars per share)	$ 2.66	$ 5.27	$ 5.33
Exercise price (in dollars per share)	$ 3.55	$ 7.46	$ 7.23
Expected life of option (in years)	5 years 9 months 18 days	5 years 9 months 18 days	5 years 9 months 18 days
Risk-free interest rate	2.10%	1.50%	1.70%
Expected volatility	91.90%	93.70%	90.70%
Dividend yield	0.00%	0.00%	0.00%