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Equity Instruments - Summary of Stock Options Outstanding and Exercisable (Detail)
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of Options Outstanding | shares 5,426,165
Weighted Average Exercise Price $ 1.99
Weighted Average Remaining Contractual Lives 4 years 7 months 24 days
$0.48 - $2.00[Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of Options Outstanding | shares 3,293,423
Weighted Average Exercise Price $ 0.82
Range of Exercise Prices Lower 0.48
Range of Exercise Prices Upper $ 2.00
Weighted Average Remaining Contractual Lives 5 years 7 months 10 days
$2.01 - $5.00 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of Options Outstanding | shares 1,750,000
Weighted Average Exercise Price $ 3.07
Range of Exercise Prices Lower 2.01
Range of Exercise Prices Upper $ 5.00
Weighted Average Remaining Contractual Lives 2 years 11 months 27 days
$5.01 - $8.93 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of Options Outstanding | shares 382,742
Weighted Average Exercise Price $ 7.13
Range of Exercise Prices Lower 5.01
Range of Exercise Prices Upper $ 8.62
Weighted Average Remaining Contractual Lives 3 years 11 months 19 days