Investment Securities - Reconciliation of Available-for-Sale and Held-to-Maturity Securities in Continuous Unrealized Loss Position (Detail) $ in Thousands	Jun. 30, 2019 USD ($) Security	Dec. 31, 2018 USD ($) Security
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	$ 695	$ 33,973
Available for Sale, Less Than 12 Months, Unrealized Losses	1	278
Available for Sale, 12 Months or Longer, Fair Value	277,161	476,622
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 2,523	$ 11,923
Available for Sale, Number of Securities (in shares) | Security	109	220
Available for Sale, Total, Fair Value	$ 277,856	$ 510,595
Available for Sale, Total, Unrealized Losses	2,524	12,201
Held to Maturity, Less Than 12 Months, Fair Value	3,641	13,971
Held to Maturity, Less Than 12 Months, Unrealized Losses	11	185
Held to Maturity, 12 Months or Longer, Fair Value	48,110	103,507
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 424	$ 2,811
Held to Maturity, Number of Securities (in shares) | Security	25	72
Held to Maturity, Total, Fair Value	$ 51,751	$ 117,478
Held to Maturity, Total, Unrealized Losses	435	2,996
U.S. Treasury and U.S. government agencies
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	0	20,588
Available for Sale, Less Than 12 Months, Unrealized Losses	0	216
Available for Sale, 12 Months or Longer, Fair Value	77,646	120,338
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 601	$ 2,352
Available for Sale, Number of Securities (in shares) | Security	15	27
Available for Sale, Total, Fair Value	$ 77,646	$ 140,926
Available for Sale, Total, Unrealized Losses	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	16,053	32,348
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 65	$ 677
Held to Maturity, Number of Securities (in shares) | Security	3	6
Held to Maturity, Total, Fair Value	$ 16,053	$ 32,348
Held to Maturity, Total, Unrealized Losses	65	677
Mortgage-backed securities, residential
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	695	10,119
Available for Sale, Less Than 12 Months, Unrealized Losses	1	58
Available for Sale, 12 Months or Longer, Fair Value	185,852	316,851
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 1,856	$ 8,785
Available for Sale, Number of Securities (in shares) | Security	79	139
Available for Sale, Total, Fair Value	$ 186,547	$ 326,970
Available for Sale, Total, Unrealized Losses	1,857	8,843
Held to Maturity, Less Than 12 Months, Fair Value	3,641	8,325
Held to Maturity, Less Than 12 Months, Unrealized Losses	11	59
Held to Maturity, 12 Months or Longer, Fair Value	25,863	53,761
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 303	$ 1,779
Held to Maturity, Number of Securities (in shares) | Security	20	36
Held to Maturity, Total, Fair Value	$ 29,504	$ 62,086
Held to Maturity, Total, Unrealized Losses	314	1,838
Mortgage-backed securities, multifamily
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	0	1,977
Available for Sale, Less Than 12 Months, Unrealized Losses	0	2
Available for Sale, 12 Months or Longer, Fair Value	4,945	12,911
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 25	$ 202
Available for Sale, Number of Securities (in shares) | Security	1	4
Available for Sale, Total, Fair Value	$ 4,945	$ 14,888
Available for Sale, Total, Unrealized Losses	25	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	1,018	1,818
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 9	$ 35
Held to Maturity, Number of Securities (in shares) | Security	1	2
Held to Maturity, Total, Fair Value	$ 1,018	$ 1,818
Held to Maturity, Total, Unrealized Losses	9	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	8,718	26,522
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 41	$ 584
Available for Sale, Number of Securities (in shares) | Security	14	50
Available for Sale, Total, Fair Value	$ 8,718	$ 27,811
Available for Sale, Total, Unrealized Losses	41	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	5,176	15,580
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 47	$ 320
Held to Maturity, Number of Securities (in shares) | Security	1	27
Held to Maturity, Total, Fair Value	$ 5,176	$ 17,344
Held to Maturity, Total, Unrealized Losses	$ 47	328
Other debt securities
Investment [Line Items]
Held to Maturity, Less Than 12 Months, Fair Value		3,882
Held to Maturity, Less Than 12 Months, Unrealized Losses		118
Held to Maturity, 12 Months or Longer, Fair Value		0
Held to Maturity, 12 Months or Longer, Unrealized Losses		$ 0
Held to Maturity, Number of Securities (in shares) | Security		1
Held to Maturity, Total, Fair Value		$ 3,882
Held to Maturity, Total, Unrealized Losses		$ 118