Derivative Instruments and Other Hedging Activities - Schedule of Outstanding Derivative Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative Assets - Fair Value	$ 283,525	$ 104,151
Derivative Liabilities - Fair Value	23,798	11,799
Designated as Hedging Instruments
Derivative [Line Items]
Derivative Assets - Fair Value	41,200	18,967
Derivative Liabilities - Fair Value	11	0
Other Assets | Designated as Hedging Instruments | Interest rate contracts
Derivative [Line Items]
Derivative Assets - Fair Value	41,200	18,967
Other Assets | Not Designated as Hedging Instruments
Derivative [Line Items]
Derivative Assets - Fair Value	242,325	85,184
Other Assets | Not Designated as Hedging Instruments | Customer swaps - upstream
Derivative [Line Items]
Derivative Assets - Fair Value	18	9
Other Assets | Not Designated as Hedging Instruments | Interest rate contracts
Derivative [Line Items]
Derivative Assets - Fair Value	222,769	77,934
Other Assets | Not Designated as Hedging Instruments | Forward sales contracts
Derivative [Line Items]
Derivative Assets - Fair Value	1,987	420
Other Assets | Not Designated as Hedging Instruments | Written and purchased options
Derivative [Line Items]
Derivative Assets - Fair Value	17,364	6,755
Other Assets | Not Designated as Hedging Instruments | Other contracts
Derivative [Line Items]
Derivative Assets - Fair Value	187	66
Other Liabilities | Designated as Hedging Instruments | Interest rate contracts
Derivative [Line Items]
Derivative Liabilities - Fair Value	11	0
Other Liabilities | Not Designated as Hedging Instruments
Derivative [Line Items]
Derivative Liabilities - Fair Value	23,787	11,799
Other Liabilities | Not Designated as Hedging Instruments | Customer swaps - upstream
Derivative [Line Items]
Derivative Liabilities - Fair Value	10,510	5,055
Other Liabilities | Not Designated as Hedging Instruments | Interest rate contracts
Derivative [Line Items]
Derivative Liabilities - Fair Value	18	1,680
Other Liabilities | Not Designated as Hedging Instruments | Forward sales contracts
Derivative [Line Items]
Derivative Liabilities - Fair Value	10,656	986
Other Liabilities | Not Designated as Hedging Instruments | Written and purchased options
Derivative [Line Items]
Derivative Liabilities - Fair Value	1,849	3,899
Other Liabilities | Not Designated as Hedging Instruments | Other contracts
Derivative [Line Items]
Derivative Liabilities - Fair Value	$ 754	$ 179