Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	$ 406,574	$ 268,637
Liability derivatives, Fair value	301,569	162,650
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	364,903	222,901
Liability derivatives, Fair value	298,326	161,994
Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	41,671	45,736
Liability derivatives, Fair value	3,243	656
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	41,259	43,892
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	428	533
Liability derivatives, Fair value	2,413	846
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	412	1,844
Liability derivatives, Fair value	3,243	656
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	16,929	10,282
Liability derivatives, Fair value	44	403
Interest Rate Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	329,739	203,517
Liability derivatives, Fair value	278,981	153,723
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	17,807	8,569
Liability derivatives, Fair value	$ 16,888	$ 7,022