Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 571,278	$ 148,862
Liability Derivatives, Fair Value	103,750	190,686
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	569,892	142,242
Liability Derivatives, Fair Value	95,633	184,252
Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	1,386	6,620
Liability Derivatives, Fair Value	8,117	6,434
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	47	5,530
Liability Derivatives, Fair Value	6,189
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	2,079	3,702
Liability Derivatives, Fair Value	13,402	4,535
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	1,339	1,090
Liability Derivatives, Fair Value	1,928	6,434
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	24,463	9,304
Liability Derivatives, Fair Value	189	1,592
Interest Rate Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	532,070	118,687
Liability Derivatives, Fair Value	72,098	169,255
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	11,280	10,549
Liability Derivatives, Fair Value	$ 9,944	$ 8,870