Soft Dollar Arrangements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Soft Dollar Arrangements [Abstract]
Soft dollar credits	$ 263	$ 152	$ 690	$ 554