Investment Securities - Reconciliation of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 153,646	$ 139,685
Gross Unrealized Gains	282	593
Gross Unrealized Losses	(2,996)	(1,590)
Fair Value	150,932	138,688
Debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,000	6,004
Gross Unrealized Gains	0	14
Gross Unrealized Losses	(118)	0
Fair Value	4,882	6,018
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	37,909	43,318
Gross Unrealized Gains	113	306
Gross Unrealized Losses	(328)	(188)
Fair Value	37,694	43,436
Mortgage-backed securities, multifamily
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,853	1,957
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(35)	(22)
Fair Value	1,818	1,935
Mortgage-backed securities, residential
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	75,859	54,991
Gross Unrealized Gains	169	249
Gross Unrealized Losses	(1,838)	(978)
Fair Value	74,190	54,262
U.S. government agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	33,025	33,415
Gross Unrealized Gains	0	24
Gross Unrealized Losses	(677)	(402)
Fair Value	$ 32,348	$ 33,037