Annual report pursuant to Section 13 and 15(d)

Off-Balance-Sheet Risk and Concentration of Credit Risk (Detail)

v3.19.1
Off-Balance-Sheet Risk and Concentration of Credit Risk (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Off-Balance-Sheet Risk and Concentration of Credit Risk [Abstract]      
Receivables from clearing brokers $ 24,068 $ 48,543 $ 48,543