Leases - Schedule of Components of Occupancy Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease Cost [Line Items]
Net lease cost	$ 13,465	$ 11,044
Other, net [Member]
Lease Cost [Line Items]
Operating lease cost for subleased/assigned properties	2,404	2,422
Sublease income for subleased/assigned properties	(2,420)	(2,422)
Occupancy [Member]
Lease Cost [Line Items]
Operating lease cost	13,455	10,875
Variable lease costs	$ 26	$ 169