Derivatives - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Derivatives	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Derivatives	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Risk participation Agreements [Line Items]
HedgedItemsOfCashFlowHedge	$ 65,000		$ 65,000
Derivative, Net Hedge Ineffectiveness Gain (Loss)	$ 221	$ 0
Risk Participation Agreements Purchased [Domain]
Risk participation Agreements [Line Items]
Number of interest rate swaps | Derivatives	50		50
Risk Participation Agreements Sold [Domain]
Risk participation Agreements [Line Items]
Number of interest rate swaps | Derivatives	12		12
Forward Contracts [Member]
Risk participation Agreements [Line Items]
Derivative, Net Hedge Ineffectiveness Gain (Loss)	$ 125	61	$ 96	$ (34)
Derivative Liability, Cost Basis, Gross Asset	7,600		7,600		$ 14,300
Derivative Liability, Fair Value, Gross Asset	8,200		8,200		14,700
Derivative Liability, Notional Amount, Gross Asset	16,700		16,700		13,800
Forward Contracts [Member] | Designated as Hedging Instrument [Member]
Risk participation Agreements [Line Items]
Derivative, Fair Value, Net	77		77		(19)
Derivative, Notional Amount	19,000		19,000		17,000
Interest Rate Contract [Member]
Risk participation Agreements [Line Items]
Derivative, Net Hedge Ineffectiveness Gain (Loss)			(432)	0
Foreign Exchange [Member]
Risk participation Agreements [Line Items]
Derivative, Net Hedge Ineffectiveness Gain (Loss)	2	2	10	3
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member]
Risk participation Agreements [Line Items]
Derivative, Fair Value, Net	(6)		(6)		70
Derivative, Notional Amount	4,058		4,058		10,077
Derivative Liability, Cost Basis, Gross Asset	4,000		4,000		10,000
Derivative Liability, Fair Value, Gross Asset	4,000		4,000		10,100
Interest Rate Swap [Member]
Risk participation Agreements [Line Items]
Derivative Instruments Designated As Hedging Instruments Interest Income	(193)	35	(424)	420
Derivative, Net Hedge Ineffectiveness Gain (Loss)	0	$ 9	10	$ 82
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Risk participation Agreements [Line Items]
Derivative, Fair Value, Net	294		294		(459)
Derivative, Notional Amount	$ 65,000		$ 65,000		$ 150,000