Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation Plans - Stock-Based Compensation Expense (Detail)

v3.19.1
Stock-Based Compensation Plans - Stock-Based Compensation Expense (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Allocated share-based compensation expense $ 2,341 $ 2,613
Employee Stock Purchase Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Allocated share-based compensation expense 30 39
Restricted Stock Awards [Member] | Non-Employee Directors [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Allocated share-based compensation expense 170 111
Restricted Stock Units [Member] | Employees [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Allocated share-based compensation expense 1,345 953
Restricted Stock Units [Member] | Independent Contractors, Prior to Adoption of New Standard [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Allocated share-based compensation expense $ 796  
Share-based compensation expense - Independent contractors   $ 1,510