Investment Securities - Reconciliation of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 151,115	$ 153,646
Gross Unrealized Gains	1,581	282
Gross Unrealized Losses	(201)	(2,996)
Investment securities held to maturity, Fair Value	152,495	150,932
U.S. government agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	31,974	33,025
Gross Unrealized Gains	234	0
Gross Unrealized Losses	(18)	(677)
Investment securities held to maturity, Fair Value	32,190	32,348
Mortgage-backed securities, residential
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	81,503	75,859
Gross Unrealized Gains	823	169
Gross Unrealized Losses	(148)	(1,838)
Investment securities held to maturity, Fair Value	82,178	74,190
Mortgage-backed securities, multifamily
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,775	1,853
Gross Unrealized Gains	15	0
Gross Unrealized Losses	(5)	(35)
Investment securities held to maturity, Fair Value	1,785	1,818
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	29,363	37,909
Gross Unrealized Gains	468	113
Gross Unrealized Losses	(30)	(328)
Investment securities held to maturity, Fair Value	29,801	37,694
Debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	6,500	5,000
Gross Unrealized Gains	41	0
Gross Unrealized Losses	0	(118)
Investment securities held to maturity, Fair Value	$ 6,541	$ 4,882