Fair Value Measurements (Narrative) (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023	Jan. 11, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Remaining unfunded commitment				$ 1,724,000
Broker dealer deposit program, fair value	$ 2,500,000,000	$ 2,500,000,000
Unused commitments to extend credit	11,186,942,000	11,186,942,000		11,671,663,000
Loans transferred to held for sale, fair value	9,200,000	9,200,000		0
Loans in process of foreclosure	21,500,000	21,500,000
Value under fair value options	1,800,000	1,800,000		1,991,000
Write-ups due to observable price changes	300,000	300,000
Write-downs due to impairment	0	0
interLINK
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent consideration			$ 16,000,000
Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	3,300,000	3,300,000		2,300,000
Rabbi Trust
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	10,200,000	10,200,000		10,000,000
Alternative investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	27,000,000	27,000,000		82,700,000
Carrying amount of alternative investments	600,000	600,000		400,000
Remaining unfunded commitment	0	0
Write-down	100,000	200,000
Alternative investments carrying amount	28,500,000	28,500,000		89,200,000
Alternative investments | Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unused commitments to extend credit	48,400,000	48,400,000		42,800,000
Unused commitments to extend credit, fair value	$ 1,900,000	$ 1,900,000		$ 5,900,000