Premises and Equipment (Narrative) (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Property, Plant and Equipment [Line Items]
Depreciation		$ 49,900	$ 41,000	$ 37,200
Operating leases, rent expense, net		46,000	42,100	31,100
Operating Lease, Right-of-Use Asset		292,087	297,736		$ 170,500
Operating lease, payments		31,600	27,500
Recognition of right of use asset related to the new corporate headquarters facility	$ 121,700
Recognition of operating lease liability related to the new corporate headquarters facility	$ 121,700
Current period amortization of deferred gain			1,400	2,800
Other Liabilities [Member]
Property, Plant and Equipment [Line Items]
Operating lease, liability		323,044	323,700		$ 174,400
Partnership Interest [Member]
Property, Plant and Equipment [Line Items]
Operating leases, rent expense, net		$ 9,800	$ 5,900	$ 464