Compensation and Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amount Recognized In Net Periodic Benefit Cost And Other Comprehensive Income Loss Before Tax [Abstract]
Service cost	$ 39	$ 39	$ 39
Interest cost	542	581	615
Expected return on plan assets	(860)	(839)	(848)
Amortization of prior service cost	25	25	25
Amortization of (gain)/loss	299	234	248
Net periodic benefit cost	$ 45	$ 40	$ 79