Securities Owned/Sold but Not Yet Purchased - Schedule of Securities Owned/Sold But Not Yet Purchased (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities Owned Total	$ 17,319	$ 8,873
Securities Sold, but not yet Purchased Total	582	1,698
Trading Securities [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities Owned Total	17,319	8,873
Securities Sold, but not yet Purchased Total	$ 582	$ 1,698