Investment Securities - Reconciliation of Available-for-Sale and Held-to-Maturity Securities in Continuous Unrealized Loss Position (Detail) $ in Thousands	Sep. 30, 2019 USD ($) Security	Dec. 31, 2018 USD ($) Security
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	$ 101,108	$ 33,973
Available for Sale, Less Than 12 Months, Unrealized Losses	398	278
Available for Sale, 12 Months or Longer, Fair Value	171,190	476,622
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 1,547	$ 11,923
Available for Sale, Number of Securities (in shares) | Security	99	220
Available for Sale, Total, Fair Value	$ 272,298	$ 510,595
Available for Sale, Total, Unrealized Losses	1,945	12,201
Held to Maturity, Less Than 12 Months, Fair Value	7,783	13,971
Held to Maturity, Less Than 12 Months, Unrealized Losses	12	185
Held to Maturity, 12 Months or Longer, Fair Value	24,822	103,507
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 189	$ 2,811
Held to Maturity, Number of Securities (in shares) | Security	18	72
Held to Maturity, Total, Fair Value	$ 32,605	$ 117,478
Held to Maturity, Total, Unrealized Losses	201	2,996
U.S. Treasury and U.S. government agencies
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	5,180	20,588
Available for Sale, Less Than 12 Months, Unrealized Losses	31	216
Available for Sale, 12 Months or Longer, Fair Value	56,134	120,338
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 461	$ 2,352
Available for Sale, Number of Securities (in shares) | Security	12	27
Available for Sale, Total, Fair Value	$ 61,314	$ 140,926
Available for Sale, Total, Unrealized Losses	492	2,568
Held to Maturity, Less Than 12 Months, Fair Value	3,799	0
Held to Maturity, Less Than 12 Months, Unrealized Losses	6	0
Held to Maturity, 12 Months or Longer, Fair Value	5,129	32,348
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 12	$ 677
Held to Maturity, Number of Securities (in shares) | Security	2	6
Held to Maturity, Total, Fair Value	$ 8,928	$ 32,348
Held to Maturity, Total, Unrealized Losses	18	677
Mortgage-backed securities, residential
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	84,842	10,119
Available for Sale, Less Than 12 Months, Unrealized Losses	284	58
Available for Sale, 12 Months or Longer, Fair Value	106,968	316,851
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 1,057	$ 8,785
Available for Sale, Number of Securities (in shares) | Security	73	139
Available for Sale, Total, Fair Value	$ 191,810	$ 326,970
Available for Sale, Total, Unrealized Losses	1,341	8,843
Held to Maturity, Less Than 12 Months, Fair Value	3,984	8,325
Held to Maturity, Less Than 12 Months, Unrealized Losses	6	59
Held to Maturity, 12 Months or Longer, Fair Value	13,516	53,761
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 142	$ 1,779
Held to Maturity, Number of Securities (in shares) | Security	14	36
Held to Maturity, Total, Fair Value	$ 17,500	$ 62,086
Held to Maturity, Total, Unrealized Losses	148	1,838
Mortgage-backed securities, multifamily
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	8,236	1,977
Available for Sale, Less Than 12 Months, Unrealized Losses	80	2
Available for Sale, 12 Months or Longer, Fair Value	4,916	12,911
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 12	$ 202
Available for Sale, Number of Securities (in shares) | Security	3	4
Available for Sale, Total, Fair Value	$ 13,152	$ 14,888
Available for Sale, Total, Unrealized Losses	92	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	1,007	1,818
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 5	$ 35
Held to Maturity, Number of Securities (in shares) | Security	1	2
Held to Maturity, Total, Fair Value	$ 1,007	$ 1,818
Held to Maturity, Total, Unrealized Losses	5	35
Obligations of states and political subdivisions
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	2,850	1,289
Available for Sale, Less Than 12 Months, Unrealized Losses	3	2
Available for Sale, 12 Months or Longer, Fair Value	3,172	26,522
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 17	$ 584
Available for Sale, Number of Securities (in shares) | Security	11	50
Available for Sale, Total, Fair Value	$ 6,022	$ 27,811
Available for Sale, Total, Unrealized Losses	20	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	5,170	15,580
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 30	$ 320
Held to Maturity, Number of Securities (in shares) | Security	1	27
Held to Maturity, Total, Fair Value	$ 5,170	$ 17,344
Held to Maturity, Total, Unrealized Losses	$ 30	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