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Equity - Schedule of Stock Option Activity (Detail) - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Stockholders Equity Note [Abstract]    
Number of Shares, Beginning balance 4,535,681 2,628,749
Number of Shares, Options granted 1,461,715 2,034,525
Number of Shares, Options expired (91,813) (127,593)
Number of Shares, Ending balance 5,905,583 4,535,681
Weighted Avg. Exercise Price, Beginning balance $ 3.31 $ 1.31
Weighted Avg. Exercise Price, Options granted 1.60 6.21
Weighted Avg.Exercise Price, Ending balance $ 2.94 $ 3.31