Leases - Schedule of Components of Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Occupancy and equipment
Schedule Of Lease Expense [Line Items]
Operating lease cost	$ 10,589	$ 10,798	$ 21,595	$ 20,664
Amortization on ROU assets	18	0	18	0
Occupancy and equipment | Disposal Group, Held-for-sale, Not Discontinued Operations | Brokerage Insurance
Schedule Of Lease Expense [Line Items]
Operating lease cost	1,080		2,193
Interest expense
Schedule Of Lease Expense [Line Items]
Interest on lease liabilities	$ 3	$ 0	$ 3	$ 0