Derivative Instruments and Other Hedging Activities - Reconciliation of Gross Amounts in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivative assets
Gross derivative assets	$ 46,828	$ 24,174
Gross amounts not offset in the Balance Sheet, derivatives	(824)	(619)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	46,004	23,555
Derivative liabilities
Gross derivative liabilities	15,212	21,288
Gross amounts not offset in the Balance Sheet, derivatives	(824)	(619)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative liabilities	14,388	20,669
Written and purchased options
Derivative assets
Gross derivative assets	4,406	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	4,406	3,285
Derivative liabilities
Gross derivative liabilities	4,406	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	4,406	3,285
Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets	6,920	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	6,920	3,469
Not Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets	35,502	17,420
Gross amounts not offset in the Balance Sheet, derivatives	(824)	(619)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	34,678	16,801
Derivative liabilities
Gross derivative liabilities	10,806	18,003
Gross amounts not offset in the Balance Sheet, derivatives	(824)	(619)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative liabilities	$ 9,982	$ 17,384