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Fair Value - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Apr. 28, 2017
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Fair Value Measurements Disclosure [Line Items]        
Transfers of assets between Level 1, Level 2, and Level 3 of the fair value hierarchy   $ 0   $ 0
Transfers of liabilities between Level 1, Level 2, and Level 3 of the fair value hierarchy   $ 0   $ 0
Warrants to purchase common shares 24,900,000      
Common stock, par value (in dollars per share) $ 0.001 $ 0.001   $ 0.001
Offering price 1.00      
Change in fair value of warrant liabilities   $ 1,829,000    
Series A Warrant [Member]        
Fair Value Measurements Disclosure [Line Items]        
Warrants, exercise price $ 1.00      
Warrant expiration date Oct. 31, 2017      
Series A Warrant [Member] | Black-Scholes Merton Model [Member]        
Fair Value Measurements Disclosure [Line Items]        
Estimated fair value of warrants $ 2,500,000      
Fair value input, term 1 year      
Fair value input, risk free rate 1.07%      
Fair value input, dividends $ 0      
Fair value input, volatility 73.14%      
Fair value input, share price $ 0.65      
Series B Warrant [Member]        
Fair Value Measurements Disclosure [Line Items]        
Warrants, exercise price $ 1.00      
Estimated fair value of warrants $ 6,200,000 $ 11,700,000   $ 14,100,000
Fair value input, term 5 years 4 years 29 days   4 years 3 months 29 days
Fair value input, risk free rate 1.81% 2.48%   2.13%
Fair value input, volatility 73.14% 85.60%   80.60%
Fair value input, share price $ 0.65 $ 1.70   $ 1.93
Common Stock [Member]        
Fair Value Measurements Disclosure [Line Items]        
Number of common stock or warrants in each unit 1      
Common Stock [Member] | Series A Warrant [Member]        
Fair Value Measurements Disclosure [Line Items]        
Number of common stock or warrants in each unit 1      
Common Stock [Member] | Series B Warrant [Member]        
Fair Value Measurements Disclosure [Line Items]        
Number of common stock or warrants in each unit 0.75      
Senhance Surgical Robotic System Acquisition [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value of contingent consideration   $ 600,000 $ 1,200,000