Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 144,199	$ 295,069
Liability Derivatives, Fair Value	143,243	176,857
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	135,601	249,988
Liability Derivatives, Fair Value	140,922	175,510
Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	8,598	45,081
Liability Derivatives, Fair Value	2,321	1,347
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	7,773	11,892
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	4,126	5,210
Liability Derivatives, Fair Value	1,582	399
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	825	33,189
Liability Derivatives, Fair Value	2,321	1,347
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	16,847	8,060
Liability Derivatives, Fair Value	645	735
Interest Rate Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	109,996	228,810
Liability Derivatives, Fair Value	134,919	167,737
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	4,632	7,908
Liability Derivatives, Fair Value	$ 3,776	$ 6,639