Investment Securities - Reconciliation of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 159,308	$ 153,646
Gross Unrealized Gains	520	282
Gross Unrealized Losses	(1,609)	(2,996)
Fair Value	158,219	150,932
U.S. government agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	32,461	33,025
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(360)	(677)
Fair Value	32,101	32,348
Mortgage-backed securities, residential
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	82,070	75,859
Gross Unrealized Gains	246	169
Gross Unrealized Losses	(1,033)	(1,838)
Fair Value	81,283	74,190
Mortgage-backed securities, multifamily
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,827	1,853
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(19)	(35)
Fair Value	1,808	1,818
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	36,450	37,909
Gross Unrealized Gains	274	113
Gross Unrealized Losses	(127)	(328)
Fair Value	36,597	37,694
Debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	6,500	5,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(70)	(118)
Fair Value	$ 6,430	$ 4,882