Investment Securities - Reconciliation of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 664,252	$ 649,741
Gross Unrealized Gains	2,068	1,078
Gross Unrealized Losses	(7,082)	(12,201)
Fair Value	659,238	638,618
U.S. Treasury and U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	141,088	143,495
Gross Unrealized Gains	94	0
Gross Unrealized Losses	(1,601)	(2,568)
Fair Value	139,581	140,927
Mortgage-backed securities, residential
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	442,358	434,208
Gross Unrealized Gains	1,473	779
Gross Unrealized Losses	(5,204)	(8,843)
Fair Value	438,627	426,144
Mortgage-backed securities, multifamily
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,956	21,087
Gross Unrealized Gains	135	67
Gross Unrealized Losses	(82)	(204)
Fair Value	31,009	20,950
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	44,850	45,951
Gross Unrealized Gains	362	140
Gross Unrealized Losses	(195)	(586)
Fair Value	45,017	45,505
Debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,000	5,000
Gross Unrealized Gains	4	92
Gross Unrealized Losses	0	0
Fair Value	$ 5,004	$ 5,092