Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Marketable Securities [Abstract]
Fair value of securities owned	$ 200		$ 14,200
Realized and unrealized net gains on marketable securities	300	$ 2,500
Marketable securities sold at fair value	14,200	4,600
Purchase of marketable securities	$ 0	$ 0