Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value of Derivatives
Derivative instruments	$ 12,570	$ 31,265
Derivative Liability	42,764	25,154
Notional Amount of Derivatives
Derivative assets	2,226,863	1,609,472
Derivative liabilities	1,717,782	1,721,752
Designated as Hedging Instruments
Fair Value of Derivatives
Derivative instruments	48	0
Derivative Liability	0	0
Notional Amount of Derivatives
Derivative assets	258,500	0
Derivative liabilities	0	108,500
Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	258,500	0
Derivative liabilities	0	108,500
Designated as Hedging Instruments | Interest rate contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	48	0
Designated as Hedging Instruments | Interest rate contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	0	0
Not Designated as Hedging Instruments
Notional Amount of Derivatives
Derivative assets	1,968,363	1,609,472
Derivative liabilities	1,717,782	1,613,252
Not Designated as Hedging Instruments | Other Assets
Fair Value of Derivatives
Derivative instruments	12,522	31,265
Not Designated as Hedging Instruments | Other Liabilities
Fair Value of Derivatives
Derivative Liability	42,764	25,154
Not Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	1,489,111	1,218,464
Derivative liabilities	1,489,111	1,218,464
Not Designated as Hedging Instruments | Interest rate contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	3,665	20,446
Not Designated as Hedging Instruments | Interest rate contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	37,417	16,191
Not Designated as Hedging Instruments | Foreign exchange contracts
Notional Amount of Derivatives
Derivative assets	933	268
Derivative liabilities	933	268
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	13	7
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	13	7
Not Designated as Hedging Instruments | Forward sales contracts
Notional Amount of Derivatives
Derivative assets	169,276	82,347
Derivative liabilities	21,684	142,578
Not Designated as Hedging Instruments | Forward sales contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	1,084	136
Not Designated as Hedging Instruments | Forward sales contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	44	279
Not Designated as Hedging Instruments | Written and purchased options
Notional Amount of Derivatives
Derivative assets	275,473	278,638
Derivative liabilities	143,912	165,198
Not Designated as Hedging Instruments | Written and purchased options | Other Assets
Fair Value of Derivatives
Derivative instruments	7,754	10,654
Not Designated as Hedging Instruments | Written and purchased options | Other Liabilities
Fair Value of Derivatives
Derivative Liability	5,282	8,656
Not Designated as Hedging Instruments | Other contracts
Notional Amount of Derivatives
Derivative assets	33,570	29,755
Derivative liabilities	62,142	86,744
Not Designated as Hedging Instruments | Other contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	6	22
Not Designated as Hedging Instruments | Other contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	$ 8	$ 21