Annual report pursuant to Section 13 and 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
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense - Independent contractors $ 7,009 $ 4,870 $ 3,314
Allocated share-based compensation expense 11,983 9,145 7,035
Employee Stock Purchase Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share-based compensation expense 109 128 169
Restricted Stock Awards [Member] | Non-Employee Directors [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share-based compensation expense 632 397 422
Restricted Stock Units [Member] | Employees [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share-based compensation expense $ 4,233 $ 3,750 $ 3,130