Related Party Transactions (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended	12 Months Ended
	Feb. 12, 2018	Mar. 15, 2017	Sep. 08, 2016	Mar. 31, 2018	Dec. 31, 2017
Related Party Transactions
Issuance of stock (in shares)				3,592,858
Follow On Offering
Related Party Transactions
Issuance of stock (in shares)	3,142,858
Share price (in dollars per share)	$ 7.00
Net proceeds	$ 23.1
Overallotment
Related Party Transactions
Issuance of stock (in shares)	450,000		27,755
Share price (in dollars per share)			$ 10.00
Private placement
Related Party Transactions
Issuance of stock (in shares)		1,324,256
Net proceeds		$ 11.2
1 Officer
Related Party Transactions
Issuance of stock (in shares)				14,286
Net proceeds				$ 0.1
Investors Related To Board Member And Officers
Related Party Transactions
Issuance of stock (in shares)				71,429
Net proceeds				$ 0.5
Three Board Members | Private placement
Related Party Transactions
Issuance of stock (in shares)					56,678
Net proceeds					$ 0.5
1 investor related to 1 board member | Private placement
Related Party Transactions
Issuance of stock (in shares)					52,798
Net proceeds					$ 0.5