Securities - Components of Available for Sale Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 309,405	$ 246,426
Available-for-sale securities, Gross unrealized gains	6,464	277
Available-for-sale securities, Gross unrealized losses	(848)	(5,060)
Available-for-sale securities, Total fair value	315,021	241,643
U.S. Treasury and Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	59,191	97,785
Available-for-sale securities, Gross unrealized gains	2,244
Available-for-sale securities, Gross unrealized losses		(2,204)
Available-for-sale securities, Total fair value	61,435	95,581
States and Municipalities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	34,999	48,167
Available-for-sale securities, Gross unrealized gains	1,494	107
Available-for-sale securities, Gross unrealized losses		(528)
Available-for-sale securities, Total fair value	36,493	47,746
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	13,174	2,000
Available-for-sale securities, Gross unrealized gains	180	4
Available-for-sale securities, Gross unrealized losses	(1)
Available-for-sale securities, Total fair value	13,353	2,004
Collateralized Mortgage Obligations (CMO) [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	52,883	21,979
Available-for-sale securities, Gross unrealized gains	1,861	143
Available-for-sale securities, Gross unrealized losses		(14)
Available-for-sale securities, Total fair value	54,744	22,108
Mortgage-Backed Securities (MBS) [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	149,158	76,495
Available-for-sale securities, Gross unrealized gains	685	23
Available-for-sale securities, Gross unrealized losses	(847)	(2,314)
Available-for-sale securities, Total fair value	$ 148,996	$ 74,204