Fair Value Measurements (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unused Commitments to Extend Credit	$ 7,152,331	$ 6,755,563
Equity Securities without Readily Determinable Fair Value, Upward Price Adjustment, Annual Amount	4,400
Equity Securities without Readily Determinable Fair Value, Downward Price Adjustment, Annual Amount	300
Mortgage Loans in Process of Foreclosure, Amount	7,500
Rabbi Trust [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Assets, Fair Value Disclosure	1,600
Alternative investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Assets, Fair Value Disclosure	14,100
Equity Securities, FV-NI	1,900
Equity Securities, FV-NI, Unrealized Gain (Loss)	500
Equity Securities without Readily Determinable Fair Value, Amount	25,900
Fair Value, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other Assets, Fair Value Disclosure	2,800
Fair Value, Nonrecurring [Member] | Alternative investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unused Commitments to Extend Credit	25,800
Alternative investments, written up	$ 5,800