Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2017
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common stock authorized (in shares)	200,000,000	200,000,000	200,000,000
Common stock issued (in shares)	3,845,361	2,535,766	2,026,608
Common stock outstanding (in shares)	3,845,361	2,535,766	2,026,608