Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash as collateral for derivative transactions	$ 27,200	$ 11,500
Fair Value of Derivatives
Derivative assets	41,440	32,903
Derivative instruments	24,534	15,411
Derivative liabilities	38,147	31,354
Notional Amount of Derivatives
Derivative assets	987,189	823,180
Derivative liabilities	1,297,423	1,062,436
Designated as Hedging Instrument
Fair Value of Derivatives
Derivative assets	0	0
Derivative liabilities	575	0
Notional Amount of Derivatives
Derivative assets	0	0
Derivative liabilities	108,500	0
Designated as Hedging Instrument | Interest Rate Contracts
Fair Value of Derivatives
Derivative instruments	575	0
Notional Amount of Derivatives
Derivative assets	0	0
Derivative liabilities	108,500	0
Designated as Hedging Instrument | Interest Rate Contracts | Other Assets
Fair Value of Derivatives
Derivative assets	0	0
Designated as Hedging Instrument | Interest Rate Contracts | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	575	0
Not Designated as Hedging Instruments
Fair Value of Derivatives
Derivative assets	41,440	32,903
Derivative instruments	37,572
Derivative liabilities		31,354
Notional Amount of Derivatives
Derivative assets	987,189	823,180
Derivative liabilities	1,188,923	1,062,436
Not Designated as Hedging Instruments | Interest Rate Contracts
Fair Value of Derivatives
Derivative instruments	23,959	15,411
Notional Amount of Derivatives
Derivative assets	565,820	444,703
Derivative liabilities	565,820	444,703
Not Designated as Hedging Instruments | Interest Rate Contracts | Other Assets
Fair Value of Derivatives
Derivative assets	23,960	15,434
Not Designated as Hedging Instruments | Interest Rate Contracts | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	23,960	15,434
Not Designated as Hedging Instruments | Foreign Exchange Contracts
Notional Amount of Derivatives
Derivative assets	4,392	0
Derivative liabilities	4,370	0
Not Designated as Hedging Instruments | Foreign Exchange Contracts | Other Assets
Fair Value of Derivatives
Derivative assets	4,369	0
Not Designated as Hedging Instruments | Foreign Exchange Contracts | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	4,369	0
Not Designated as Hedging Instruments | Forward Sales Contracts
Notional Amount of Derivatives
Derivative assets	55,412	15,897
Derivative liabilities	428,547	391,992
Not Designated as Hedging Instruments | Forward Sales Contracts | Other Assets
Fair Value of Derivatives
Derivative assets	452	25
Not Designated as Hedging Instruments | Forward Sales Contracts | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	3,108	2,556
Not Designated as Hedging Instruments | Written and Purchased Options
Notional Amount of Derivatives
Derivative assets	361,565	362,580
Derivative liabilities	190,186	225,741
Not Designated as Hedging Instruments | Written and Purchased Options | Other Assets
Fair Value of Derivatives
Derivative assets	12,659	17,444
Not Designated as Hedging Instruments | Written and Purchased Options | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	$ 6,135	$ 13,364