Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Stock-Based Compensation Plans - Stock-Based Compensation Expense (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense - Independent contractors $ 1,816 $ 1,081 $ 5,200 $ 2,942
Allocated share-based compensation expense 3,147 2,192 8,919 6,173
Employee Stock Purchase Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Allocated share-based compensation expense 37 31 100 106
Restricted Stock Awards [Member] | Non-Employee Directors [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Allocated share-based compensation expense 182 105 458 284
Restricted Stock Units [Member] | Employees [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Allocated share-based compensation expense $ 1,112 $ 975 $ 3,161 $ 2,841