Derivatives - Summary Information Regarding Derivatives (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
3rd Party interest rate swaps
Derivative [Line Items]
Other Assets, Notional Amount	$ 190,679	$ 110,076
Other Assets, Average Maturity (Years)	9 years 4 months 24 days	8 years 9 months 18 days
Other Assets, Wighted Average Fixed Rate	4.25%	3.87%
Other Assets, Weighted Average Variable Rate	1 Mo. LIBOR + 2.15%	1 Mo. LIBOR + 2.11%
Other Assets, Fair Value	$ 8,675	$ 3,634
Other Assets, Average Basis Spread On Variable Rate	2.15%	2.11%
Other Liabilities, Notional Amount	$ 58,754	$ 82,760
Other Liabilities, Average Maturity (Years)	10 years 9 months 18 days	11 years 6 months
Other Liabilities, Weighted Average Fixed Rate	5.15%	4.74%
Other Liabilities, Weighted Average Variable Rate	1 Mo. LIBOR + 2.12%	1 Mo. LIBOR + 2.21%
Other Liabilities, Fair Value	$ (996)	$ (1,831)
Other Liabilities, Average Basis Spread On Variable Rate	2.12%	2.21%
Customer interest rate swaps
Derivative [Line Items]
Other Assets, Notional Amount	$ 58,754	$ 82,760
Other Assets, Average Maturity (Years)	10 years 9 months 18 days	11 years 6 months
Other Assets, Wighted Average Fixed Rate	5.15%	4.74%
Other Assets, Weighted Average Variable Rate	1 Mo. LIBOR + 2.12%	1 Mo. LIBOR + 2.21%
Other Assets, Fair Value	$ 996	$ 1,831
Other Assets, Average Basis Spread On Variable Rate	2.12%	2.21%
Other Liabilities, Notional Amount	$ 190,679	$ 110,076
Other Liabilities, Average Maturity (Years)	9 years 4 months 24 days	8 years 9 months 18 days
Other Liabilities, Weighted Average Fixed Rate	4.25%	3.87%
Other Liabilities, Weighted Average Variable Rate	1 Mo. LIBOR + 2.15%	1 Mo. LIBOR + 2.11%
Other Liabilities, Fair Value	$ (8,675)	$ (3,634)
Other Liabilities, Average Basis Spread On Variable Rate	2.15%	2.11%
Interest rate swap (cash flow hedge)
Derivative [Line Items]
Other Assets, Notional Amount	$ 30,000	$ 30,000
Other Assets, Average Maturity (Years)	3 years	3 years 6 months
Other Assets, Wighted Average Fixed Rate	1.10%	1.10%
Other Assets, Weighted Average Variable Rate	3 Mo. LIBOR	3 Mo. LIBOR
Other Assets, Fair Value	$ 1,516	$ 1,090