Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 618,019	$ 1,067,985
Liability Derivatives, Fair Value	105,769	140,485
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	609,699	1,064,529
Liability Derivatives, Fair Value	104,776	131,135
Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	8,320	3,456
Liability Derivatives, Fair Value	993	9,350
Interest Rate Swap Agreements [Member] | Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	1,608	1,968
Liability Derivatives, Fair Value	224	892
Commitments to Sell Real Estate Loans [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	11,604	2,409
Liability Derivatives, Fair Value	7,813	13,868
Commitments to Sell Real Estate Loans [Member] | Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	6,712	1,488
Liability Derivatives, Fair Value	769	8,458
Mortgage-Related Commitments to Originate Real Estate Loans for Sale [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	24,459	43,599
Liability Derivatives, Fair Value	4,314	365
Interest Rate Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	565,332	1,008,913
Liability Derivatives, Fair Value	84,909	105,768
Foreign Exchange and Other Option and Futures Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	8,304	9,608
Liability Derivatives, Fair Value	$ 7,740	$ 11,134