Quarterly report pursuant to Section 13 or 15(d)

Selected Balance Sheet Data - Components of Deferred Compensation and Commissions (Detail)

v3.10.0.1
Selected Balance Sheet Data - Components of Deferred Compensation and Commissions (Detail) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Stock appreciation rights ("SARs") liability $ 1,895 $ 1,662
Deferred compensation liability 1,505 1,261
Deferred compensation and commissions, current 34,107 49,180
Stock appreciation rights ("SARs") liability 18,931 20,217
Deferred compensation liability 7,709 7,220
Deferred compensation and commissions, non-current 41,557 49,361
Current [Member]    
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Commissions payable to investment sales and financing professionals 30,707 46,257
Non-Current [Member]    
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Commissions payable to investment sales and financing professionals $ 14,917 $ 21,924