XML 56 R46.htm IDEA: XBRL DOCUMENT v3.10.0.1
Common Stock and Stock-Based Compensation Plans - Additional Information (Detail) - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
2011 Stock Incentive Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options and stock appreciation rights granted under stock incentive plans vesting rate, year one 25.00%  
Remaining shares vesting period 36 months  
Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Shares vesting period 4 years  
Stock Appreciation Rights (SARs) | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options granted percentage 400.00%  
Stock Options, SARs    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unrecognized compensation expense $ 224  
Unrecognized compensation expense, weighted-average period of recognition 1 year 2 months 12 days  
Restricted Stock Units (RSUs)    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unrecognized compensation expense $ 13,278  
Unrecognized compensation expense, weighted-average period of recognition 1 year 6 months  
Employees and non-employees award vesting, description RSUs granted to employees generally vest in three equal annual installments starting on the first anniversary of the grant date. Until the end of 2017, RSUs granted to non-employee directors would generally vest in full on the first anniversary of the grant date. Starting in 2018, RSUs granted to non-employee directors would generally vest in two equal annual installments starting on the first anniversary of the grant date.  
Non Employee Director    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options granted under stock incentive plan vesting rate, each anniversary 25.00%  
Non Employee Director | Restricted Stock Units (RSUs)    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Shares vesting period 2 years 1 year
Employee | Restricted Stock Units (RSUs)    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Shares vesting period 3 years