Annual report pursuant to Section 13 and 15(d)

Stock Based Compensation - Restricted Stock Units - Additional Information (Detail)

v3.8.0.1
Stock Based Compensation - Restricted Stock Units - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Jan. 04, 2016
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period           1,253,085
Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, award vesting period         4 years  
Employee service share-based compensation, nonvested awards, compensation not yet recognized, share-based awards other than options   $ 24,701,605       $ 24,701,605
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition           2 years 8 months 12 days
2013 Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period   53,188 117,514 308,059 351,080  
Share-based compensation arrangement by share-based payment award, award vesting period   4 years        
Non-Employee Equity Compensation Plan 2014 [Member] | Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period       8,400 48,844  
Inducement RSU Award [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period       120,000    
Share-based compensation arrangement by share-based payment award, award vesting period       4 years    
Minimum [Member] | 2013 Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, award vesting period     2 years 2 years 2 years  
Minimum [Member] | Non-Employee Equity Compensation Plan 2014 [Member] | Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, award vesting period       2 years    
Maximum [Member] | 2013 Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, award vesting period     4 years 4 years 4 years  
Maximum [Member] | Non-Employee Equity Compensation Plan 2014 [Member] | Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, award vesting period       4 years    
Mr. Gaulding [Member] | Non-Employee Equity Compensation Plan 2014 [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period 14,953          
Mr. Gaulding [Member] | Non-Employee Equity Compensation Plan 2014 [Member] | Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period         246,000