Derivative Instruments and Other Hedging Activities - Reconciliation of Gross Amounts in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivative assets
Gross derivative assets	$ 28,587	$ 28,804
Gross amounts not offset in the Balance Sheet, derivatives	(8,632)	(9,677)
Gross amounts not offset in the Balance Sheet, collateral	0	0
Net derivative assets	19,955	19,127
Derivative liabilities
Gross derivative liabilities	18,912	21,244
Gross amounts not offset in the Balance Sheet, derivatives	(8,632)	(9,677)
Gross amounts not offset in the Balance Sheet, collateral	(983)	(1,892)
Net derivative liabilities	9,297	9,675
Written and purchased options
Derivative assets
Gross derivative assets	8,835	8,085
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	8,835	8,085
Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets	19,752
Gross amounts not offset in the Balance Sheet, derivatives	(8,632)
Gross amounts not offset in the Balance Sheet, collateral	0
Net derivative assets	11,120
Derivative liabilities
Gross derivative liabilities	1,027	525
Gross amounts not offset in the Balance Sheet, derivatives	0	0
Gross amounts not offset in the Balance Sheet, collateral	0	(181)
Net derivative liabilities	1,027	344
Not Designated as Hedging Instruments | Interest rate contracts
Derivative assets
Gross derivative assets		20,719
Gross amounts not offset in the Balance Sheet, derivatives		(9,677)
Gross amounts not offset in the Balance Sheet, collateral		0
Net derivative assets		11,042
Derivative liabilities
Gross derivative liabilities	17,885	20,719
Gross amounts not offset in the Balance Sheet, derivatives	(8,632)	(9,677)
Gross amounts not offset in the Balance Sheet, collateral	(983)	(1,711)
Net derivative liabilities	$ 8,270	$ 9,331