Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value of Derivatives
Derivative Asset	$ 12,913	$ 31,265
Derivative Liability	38,607	25,154
Notional Amount of Derivatives
Derivative assets	1,985,099	1,609,472
Derivative liabilities	1,761,381	1,721,752
Designated as Hedging Instruments
Fair Value of Derivatives
Derivative Asset	305	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 Asset	305	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	1,726,599	1,609,472
Derivative liabilities	1,761,381	1,613,252
Not Designated as Hedging Instruments | Other Assets
Fair Value of Derivatives
Derivative Asset	12,608	31,265
Not Designated as Hedging Instruments | Other Liabilities
Fair Value of Derivatives
Derivative Liability	38,607	25,154
Not Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	1,340,648	1,218,464
Derivative liabilities	1,340,648	1,218,464
Not Designated as Hedging Instruments | Interest rate contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	4,083	20,446
Not Designated as Hedging Instruments | Interest rate contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	32,660	16,191
Not Designated as Hedging Instruments | Foreign exchange contracts
Notional Amount of Derivatives
Derivative assets	881	268
Derivative liabilities	881	268
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	17	7
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	17	7
Not Designated as Hedging Instruments | Forward sales contracts
Notional Amount of Derivatives
Derivative assets	45,434	82,347
Derivative liabilities	187,728	142,578
Not Designated as Hedging Instruments | Forward sales contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	114	136
Not Designated as Hedging Instruments | Forward sales contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	700	279
Not Designated as Hedging Instruments | Written and purchased options
Notional Amount of Derivatives
Derivative assets	305,931	278,638
Derivative liabilities	157,594	165,198
Not Designated as Hedging Instruments | Written and purchased options | Other Assets
Fair Value of Derivatives
Derivative Asset	8,385	10,654
Not Designated as Hedging Instruments | Written and purchased options | Other Liabilities
Fair Value of Derivatives
Derivative Liability	5,219	8,656
Not Designated as Hedging Instruments | Other contracts
Notional Amount of Derivatives
Derivative assets	33,705	29,755
Derivative liabilities	74,530	86,744
Not Designated as Hedging Instruments | Other contracts | Other Assets
Fair Value of Derivatives
Derivative Asset	9	22
Not Designated as Hedging Instruments | Other contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	$ 11	$ 21