Derivative Instruments and Other Hedging Activities - Reconciliation of Gross Amounts in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative assets
Gross derivative assets	$ 131,710	$ 24,174
Gross amounts not offset in the Balance Sheet, derivatives	(6,119)	(619)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	125,591	23,555
Derivative liabilities
Gross derivative liabilities	9,891	21,288
Gross amounts not offset in the Balance Sheet, derivatives	(6,119)	(619)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative liabilities	3,772	20,669
Written and purchased options
Derivative assets
Gross derivative assets	3,581	3,285
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	3,581	3,285
Derivative liabilities
Gross derivative liabilities	3,581	3,285
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative liabilities	3,581	3,285
Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets	23,338	3,469
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	23,338	3,469
Not Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets	104,791	17,420
Gross amounts not offset in the Balance Sheet, derivatives	(6,119)	(619)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	98,672	16,801
Derivative liabilities
Gross derivative liabilities	6,310	18,003
Gross amounts not offset in the Balance Sheet, derivatives	(6,119)	(619)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative liabilities	$ 191	$ 17,384