Derivative Instruments and Hedging Activities - Derivatives Designated as Hedging Instruments (Detail) - Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 19,224	$ 19,993
Derivative Assets	13	0
Derivative Liabilities	12	254
Net loss	(175)	(299)	$ (377)
Gain (loss) recognized in other comprehensive income (loss)	9	(141)
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	17,836	18,566
Gain (loss) recognized in other comprehensive income (loss)	9	(141)
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net loss	182	308	377
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Other Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets	13	0
Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Other Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities	0	217
Interest Rate Swap [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,388	1,427
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Other Noninterest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net loss	7	9	$ 0
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Other Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Assets	0	0
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Other Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities	$ 12	$ 37