Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	$ 361,275	$ 338,855
Liability derivatives, Fair value	242,495	212,059
Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	299,594	264,876
Liability derivatives, Fair value	237,353	207,842
Fair Value Hedges [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	61,681	73,979
Liability derivatives, Fair value	5,142	4,217
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	60,782	73,251
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	26	754
Liability derivatives, Fair value	4,162	4,330
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	899	728
Liability derivatives, Fair value	5,142	4,217
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	17,832	17,396
Liability derivatives, Fair value	185	49
Interest Rate Contracts [Member] | Derivatives Not Designated and Qualifying as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives, Fair value	268,332	215,614
Liability derivatives, Fair value	221,626	173,513
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	13,404	31,112
Liability derivatives, Fair value	$ 11,380	$ 29,950