Derivatives - Summary Information Regarding Derivatives (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
3rd Party interest rate swaps
Derivative [Line Items]
Derivatives, asset notional amount	$ 153,909,000	$ 110,076,000
Derivatives liability, notional amount	$ 164,427,000	$ 82,760,000
Derivatives, asset average maturity (years)	8 years 3 months 18 days	8 years 9 months 18 days
Derivative, liability average maturity (years)	12 years	11 years 6 months
Weighted average rate fixed, other assets	4.10%	3.87%
Weighted average rate fixed, other liabilities	5.04%	4.74%
Weighted average variable rate description, other assets	1 Mo. LIBOR + 2.13%	1 Mo. LIBOR + 2.11%
Weighted average variable rate, other liabilities	1 Mo. LIBOR + 2.05%	1 Mo. LIBOR + 2.21%
Derivatives asset, asset fair value	$ 5,329,000	$ 3,634,000
Derivative liability, liability fair value	$ (5,707,000)	$ (1,831,000)
Derivative asset, average basis spread on variable rate	2.00%	2.11%
Derivative liability, average basis spread on variable rate	2.05%	2.21%
Customer interest rate swaps
Derivative [Line Items]
Derivatives, asset notional amount	$ 164,427,000	$ 82,760,000
Derivatives liability, notional amount	$ 153,909,000	$ 110,076,000
Derivatives, asset average maturity (years)	12 years	11 years 6 months
Derivative, liability average maturity (years)	8 years 3 months 18 days	8 years 9 months 18 days
Weighted average rate fixed, other assets	5.04%	4.74%
Weighted average rate fixed, other liabilities	4.10%	3.87%
Weighted average variable rate description, other assets	1 Mo. LIBOR + 2.05%	1 Mo. LIBOR + 2.21%
Weighted average variable rate, other liabilities	1 Mo. LIBOR + 2.13%	1 Mo. LIBOR + 2.11%
Derivatives asset, asset fair value	$ 5,707,000	$ 1,831,000
Derivative liability, liability fair value	$ (5,329,000)	$ (3,634,000)
Derivative asset, average basis spread on variable rate	2.00%	2.21%
Derivative liability, average basis spread on variable rate	2.13%	2.11%
Interest rate swap (cash flow hedge)
Derivative [Line Items]
Derivatives, asset notional amount	$ 30,000,000	$ 30,000,000
Derivatives, asset average maturity (years)	2 years 6 months	3 years 6 months
Weighted average rate fixed, other assets	1.10%	1.10%
Weighted average variable rate description, other assets	3 Mo. LIBOR	3 Mo. LIBOR
Derivatives asset, asset fair value	$ 1,099,000	$ 1,090,000