Stockholders' Equity - Stock and warrants (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2018 Vote $ / shares shares	Dec. 31, 2013 shares	Dec. 31, 2017 shares
Preferred stock
Preferred stock, shares authorized	25,000,000		25,000,000
Preferred stock, shares issued	0		0
Common stock
Number of votes for each shares held | Vote	1
Warrants
Number of shares into which warrant issued during period may be converted		129,491
Warrant exercise price per share (in dollars per share) | $ / shares	$ 0.05
Contractual life of warrants	10 years
Number of shares of common stock into which warrants may be converted	110,365
Stock options.
Common stock
Number of shares reserved for future issuance	3,905,845		3,205,485
Warrants
Common stock
Number of shares reserved for future issuance	110,365		110,365
Warrants and options
Common stock
Number of shares reserved for future issuance	4,016,210		3,315,850