Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value of Derivatives
Derivative instruments	$ 51,086	$ 27,048
Derivative Liability	16,756	22,124
Notional Amount of Derivatives
Derivative assets	2,843,914	2,311,612
Derivative liabilities	2,480,018	1,991,559
Designated as Hedging Instruments
Fair Value of Derivatives
Derivative instruments	6,920	3,469
Derivative Liability	0	0
Notional Amount of Derivatives
Derivative assets	500,000	408,500
Derivative liabilities	108,500	0
Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	500,000	408,500
Derivative liabilities	108,500	0
Designated as Hedging Instruments | Interest rate contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	6,920	3,469
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	2,343,914	1,903,112
Derivative liabilities	2,371,518	1,991,559
Not Designated as Hedging Instruments | Other Assets
Fair Value of Derivatives
Derivative instruments	44,166	23,579
Not Designated as Hedging Instruments | Other Liabilities
Fair Value of Derivatives
Derivative Liability	16,756	22,124
Not Designated as Hedging Instruments | Interest rate contracts
Notional Amount of Derivatives
Derivative assets	1,290,051	701,257
Derivative liabilities	634,998	919,653
Not Designated as Hedging Instruments | Interest rate contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	35,265	16,946
Not Designated as Hedging Instruments | Interest rate contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	9,766	17,812
Not Designated as Hedging Instruments | Customer swaps - upstream
Notional Amount of Derivatives
Derivative assets	634,998	919,653
Derivative liabilities	1,290,051	701,257
Not Designated as Hedging Instruments | Customer swaps - upstream | Other Assets
Fair Value of Derivatives
Derivative instruments	237	474
Not Designated as Hedging Instruments | Customer swaps - upstream | Other Liabilities
Fair Value of Derivatives
Derivative Liability	1,040	191
Not Designated as Hedging Instruments | Foreign exchange contracts
Notional Amount of Derivatives
Derivative assets	903	1,202
Derivative liabilities	903	1,202
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	7	18
Not Designated as Hedging Instruments | Foreign exchange contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	7	18
Not Designated as Hedging Instruments | Forward sales contracts
Notional Amount of Derivatives
Derivative assets	43,567	1,140
Derivative liabilities	205,278	143,179
Not Designated as Hedging Instruments | Forward sales contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	143	630
Not Designated as Hedging Instruments | Forward sales contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	1,440	750
Not Designated as Hedging Instruments | Written and purchased options
Notional Amount of Derivatives
Derivative assets	324,345	229,333
Derivative liabilities	141,430	140,645
Not Designated as Hedging Instruments | Written and purchased options | Other Assets
Fair Value of Derivatives
Derivative instruments	8,488	5,490
Not Designated as Hedging Instruments | Written and purchased options | Other Liabilities
Fair Value of Derivatives
Derivative Liability	4,446	3,310
Not Designated as Hedging Instruments | Other contracts
Notional Amount of Derivatives
Derivative assets	50,050	50,527
Derivative liabilities	98,858	85,623
Not Designated as Hedging Instruments | Other contracts | Other Assets
Fair Value of Derivatives
Derivative instruments	26	21
Not Designated as Hedging Instruments | Other contracts | Other Liabilities
Fair Value of Derivatives
Derivative Liability	$ 57	$ 43