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Fair Value - Additional Information (Detail)
3 Months Ended 12 Months Ended
Apr. 28, 2017
USD ($)
$ / shares
shares
Mar. 31, 2019
USD ($)
$ / shares
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
$ / shares
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 | shares 24,900,000      
Offering price | $ / shares $ 1.00      
Change in fair value of warrant liabilities   106,000 $ (1,829,000)  
Series A Warrant [Member]        
Fair Value Measurements Disclosure [Line Items]        
Warrants, exercise price | $ / shares $ 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, share price | $ / shares $ 0.65      
Series A Warrant [Member] | Black-Scholes Merton Model [Member] | Measurement Input, Expected Term [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value input, term 1 year      
Series A Warrant [Member] | Black-Scholes Merton Model [Member] | Measurement Input, Risk Free Interest Rate [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value input, risk free rate 0.0107      
Series A Warrant [Member] | Black-Scholes Merton Model [Member] | Measurement Input, Expected Dividend Payment [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value input, risk free rate 0      
Series A Warrant [Member] | Black-Scholes Merton Model [Member] | Measurement Input, Price Volatility [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value input, risk free rate 0.7314      
Series B Warrant [Member]        
Fair Value Measurements Disclosure [Line Items]        
Warrants, exercise price | $ / shares $ 1.00      
Estimated fair value of warrants $ 6,200,000 $ 4,700,000   $ 4,600,000
Fair value input, share price | $ / shares $ 0.65 $ 2.38   $ 2.26
Change in fair value of warrant liabilities   $ 100,000   $ (1,800,000)
Series B Warrant [Member] | Measurement Input, Expected Term [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value input, term 5 years 3 years 29 days   3 years 3 months 25 days
Series B Warrant [Member] | Measurement Input, Risk Free Interest Rate [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value input, risk free rate 1.81 2.21   2.47
Series B Warrant [Member] | Measurement Input, Price Volatility [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value input, risk free rate 73.14 82.37   87.60
Common Stock [Member]        
Fair Value Measurements Disclosure [Line Items]        
Number of common stock or warrants in each unit | shares 1      
Common Stock [Member] | Series A Warrant [Member]        
Fair Value Measurements Disclosure [Line Items]        
Number of common stock or warrants in each unit | shares 1      
Common Stock [Member] | Series B Warrant [Member]        
Fair Value Measurements Disclosure [Line Items]        
Number of common stock or warrants in each unit | shares 0.75      
Senhance Surgical Robotic System Acquisition [Member]        
Fair Value Measurements Disclosure [Line Items]        
Fair value of contingent consideration   $ 1,000,000 $ 600,000