Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Fair Value of Derivatives
Derivative assets	$ 55,804	$ 30,486
Derivative liabilities	58,939	24,939
Notional Amount of Derivatives
Derivative assets	1,434,891	1,255,277
Derivative liabilities	1,662,508	950,105
Cash as collateral for derivative transactions	58,000	20,100
Designated as Hedging Instrument
Fair Value of Derivatives
Derivative assets	0	58
Derivative liabilities	9,649	0
Notional Amount of Derivatives
Derivative assets	0	108,500
Derivative liabilities	108,500	0
Designated as Hedging Instrument | Interest Rate Contracts
Notional Amount of Derivatives
Derivative assets	0	108,500
Derivative liabilities	108,500	0
Designated as Hedging Instrument | Interest Rate Contracts | Other Assets
Fair Value of Derivatives
Derivative assets	0	58
Designated as Hedging Instrument | Interest Rate Contracts | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	9,649	0
Not Designated as Hedging Instruments
Fair Value of Derivatives
Derivative assets	55,804	30,428
Derivative liabilities	49,290	24,939
Notional Amount of Derivatives
Derivative assets	1,434,891	1,146,777
Derivative liabilities	1,554,008	950,105
Not Designated as Hedging Instruments | Interest Rate Contracts
Notional Amount of Derivatives
Derivative assets	976,456	590,334
Derivative liabilities	976,456	590,334
Not Designated as Hedging Instruments | Interest Rate Contracts | Other Assets
Fair Value of Derivatives
Derivative assets	39,438	18,077
Not Designated as Hedging Instruments | Interest Rate Contracts | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	39,563	18,077
Not Designated as Hedging Instruments | Foreign Exchange Contracts
Notional Amount of Derivatives
Derivative assets	4,644	4,392
Derivative liabilities	4,644	4,392
Not Designated as Hedging Instruments | Foreign Exchange Contracts | Other Assets
Fair Value of Derivatives
Derivative assets	44	156
Not Designated as Hedging Instruments | Foreign Exchange Contracts | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	30	134
Not Designated as Hedging Instruments | Forward Sales Contracts
Notional Amount of Derivatives
Derivative assets	53,662	223,841
Derivative liabilities	405,697	173,430
Not Designated as Hedging Instruments | Forward Sales Contracts | Other Assets
Fair Value of Derivatives
Derivative assets	105	1,588
Not Designated as Hedging Instruments | Forward Sales Contracts | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	1,680	474
Not Designated as Hedging Instruments | Written and Purchased Options
Notional Amount of Derivatives
Derivative assets	400,129	328,210
Derivative liabilities	167,211	181,949
Not Designated as Hedging Instruments | Written and Purchased Options | Other Assets
Fair Value of Derivatives
Derivative assets	16,217	10,607
Not Designated as Hedging Instruments | Written and Purchased Options | Other Liabilities
Fair Value of Derivatives
Derivative liabilities	$ 8,017	$ 6,254