Investment Securities - Reconciliation of Available-for-Sale and Held-to-Maturity Securities in Continuous Unrealized Loss Position (Detail) $ in Thousands	Mar. 31, 2019 USD ($) Security	Dec. 31, 2018 USD ($) Security
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	$ 17,810	$ 33,973
Available for Sale, Less Than 12 Months, Unrealized Losses	88	278
Available for Sale, 12 Months or Longer, Fair Value	434,514	476,622
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 6,994	$ 11,923
Available for Sale, Number of Securities (in shares) | Security	185	220
Available for Sale, Total, Fair Value	$ 452,324	$ 510,595
Available for Sale, Total, Unrealized Losses	7,082	12,201
Held to Maturity, Less Than 12 Months, Fair Value	12,942	13,971
Held to Maturity, Less Than 12 Months, Unrealized Losses	97	185
Held to Maturity, 12 Months or Longer, Fair Value	89,341	103,507
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 1,512	$ 2,811
Held to Maturity, Number of Securities (in shares) | Security	47	72
Held to Maturity, Total, Fair Value	$ 102,283	$ 117,478
Held to Maturity, Total, Unrealized Losses	1,609	2,996
U.S. Treasury and U.S. government agencies
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	12,112	20,588
Available for Sale, Less Than 12 Months, Unrealized Losses	78	216
Available for Sale, 12 Months or Longer, Fair Value	116,126	120,338
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 1,523	$ 2,352
Available for Sale, Number of Securities (in shares) | Security	25	27
Available for Sale, Total, Fair Value	$ 128,238	$ 140,926
Available for Sale, Total, Unrealized Losses	1,601	2,568
Held to Maturity, Less Than 12 Months, Fair Value	0	0
Held to Maturity, Less Than 12 Months, Unrealized Losses	0	0
Held to Maturity, 12 Months or Longer, Fair Value	32,101	32,348
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 360	$ 677
Held to Maturity, Number of Securities (in shares) | Security	6	6
Held to Maturity, Total, Fair Value	$ 32,101	$ 32,348
Held to Maturity, Total, Unrealized Losses	360	677
Mortgage-backed securities, residential
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	719	10,119
Available for Sale, Less Than 12 Months, Unrealized Losses	1	58
Available for Sale, 12 Months or Longer, Fair Value	289,307	316,851
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 5,203	$ 8,785
Available for Sale, Number of Securities (in shares) | Security	126	139
Available for Sale, Total, Fair Value	$ 290,026	$ 326,970
Available for Sale, Total, Unrealized Losses	5,204	8,843
Held to Maturity, Less Than 12 Months, Fair Value	9,012	8,325
Held to Maturity, Less Than 12 Months, Unrealized Losses	27	59
Held to Maturity, 12 Months or Longer, Fair Value	47,210	53,761
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 1,006	$ 1,779
Held to Maturity, Number of Securities (in shares) | Security	31	36
Held to Maturity, Total, Fair Value	$ 56,222	$ 62,086
Held to Maturity, Total, Unrealized Losses	1,033	1,838
Mortgage-backed securities, multifamily
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	4,979	1,977
Available for Sale, Less Than 12 Months, Unrealized Losses	9	2
Available for Sale, 12 Months or Longer, Fair Value	12,993	12,911
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 73	$ 202
Available for Sale, Number of Securities (in shares) | Security	4	4
Available for Sale, Total, Fair Value	$ 17,972	$ 14,888
Available for Sale, Total, Unrealized Losses	82	204
Held to Maturity, Less Than 12 Months, Fair Value	0	0
Held to Maturity, Less Than 12 Months, Unrealized Losses	0	0
Held to Maturity, 12 Months or Longer, Fair Value	1,808	1,818
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 19	$ 35
Held to Maturity, Number of Securities (in shares) | Security	2	2
Held to Maturity, Total, Fair Value	$ 1,808	$ 1,818
Held to Maturity, Total, Unrealized Losses	19	35
Obligations of states and political subdivisions
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	0	1,289
Available for Sale, Less Than 12 Months, Unrealized Losses	0	2
Available for Sale, 12 Months or Longer, Fair Value	16,088	26,522
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 195	$ 584
Available for Sale, Number of Securities (in shares) | Security	30	50
Available for Sale, Total, Fair Value	$ 16,088	$ 27,811
Available for Sale, Total, Unrealized Losses	195	586
Held to Maturity, Less Than 12 Months, Fair Value	0	1,764
Held to Maturity, Less Than 12 Months, Unrealized Losses	0	8
Held to Maturity, 12 Months or Longer, Fair Value	8,222	15,580
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 127	$ 320
Held to Maturity, Number of Securities (in shares) | Security	7	27
Held to Maturity, Total, Fair Value	$ 8,222	$ 17,344
Held to Maturity, Total, Unrealized Losses	127	328
Debt securities
Investment [Line Items]
Held to Maturity, Less Than 12 Months, Fair Value	3,930	3,882
Held to Maturity, Less Than 12 Months, Unrealized Losses	70	118
Held to Maturity, 12 Months or Longer, Fair Value	0	0
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 0	$ 0
Held to Maturity, Number of Securities (in shares) | Security	1	1
Held to Maturity, Total, Fair Value	$ 3,930	$ 3,882
Held to Maturity, Total, Unrealized Losses	$ 70	$ 118