Stock Purchase Warrants (Details) $ / shares in Units, $ in Millions			3 Months Ended	12 Months Ended
	Dec. 06, 2017 $ / shares	Sep. 09, 2016 $ / shares shares	Mar. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 $ / shares	Dec. 07, 2017 holder $ / shares shares	Aug. 16, 2013 $ / shares shares
August 2013 Warrants
Stock Purchase Warrants
Exercise price (in dollars per share)						$ 4.80
Total shares issuable on exercise (in shares) | shares						365,150
Shares issued upon the exercise of warrants, value | $			$ 1.7
Assumptions used in calculating the estimated fair value of the warrants
Closing stock price (in dollars per share)			$ 9.95	$ 5.45
Expected dividend rate			0.00%	0.00%
Expected stock price volatility			75.40%	63.70%
Risk-free interest rate			2.00%	1.70%
Expected life			4 months 17 days	7 months 13 days
August 2013 Warrants | Common Stock
Stock Purchase Warrants
Shares issued upon the exercise of warrants (in shares) | shares			359,800
September 2016 Warrants
Stock Purchase Warrants
Exercise price (in dollars per share)		$ 2.25
Total shares issuable on exercise (in shares) | shares		117,074
Assumptions used in calculating the estimated fair value of the warrants
Closing stock price (in dollars per share)		$ 2.2
Expected dividend rate		0.00%
Expected stock price volatility		89.80%
Risk-free interest rate		1.40%
Expected life		6 years
December 2017 Warrants
Stock Purchase Warrants
Exercise price (in dollars per share)					$ 4.27
Total shares issuable on exercise (in shares) | shares					53,902
Number of warrant holders | holder					2
Assumptions used in calculating the estimated fair value of the warrants
Closing stock price (in dollars per share)	$ 5.10
Expected dividend rate	0.00%
Expected stock price volatility	86.40%
Risk-free interest rate	2.20%
Expected life	6 years