Investment Securities - Reconciliation of Available-for-Sale and Held-to-Maturity Securities in Continuous Unrealized Loss Position (Detail) $ in Thousands	Sep. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Investment Holdings [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	$ 157,721	$ 145,431
Available for Sale, Less Than 12 Months, Unrealized Losses	1,279	720
Available for Sale, 12 Months or Longer, Fair Value	27,249	152,543
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 387	$ 1,425
Available for Sale, Number of Securities (in shares) \| security	74	105
Available for Sale, Total, Fair Value	$ 184,970	$ 297,974
Available for Sale, Total, Unrealized Losses	1,666	2,145
Held to Maturity, Less Than 12 Months, Fair Value	119	15,657
Held to Maturity, Less Than 12 Months, Unrealized Losses	1	52
Held to Maturity, 12 Months or Longer, Fair Value	25	16,692
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 0	$ 134
Held to Maturity, Number of Securities (in shares) \| security	5	19
Held to Maturity, Total, Fair Value	$ 144	$ 32,349
Held to Maturity, Total, Unrealized Losses	1	186
U.S. Treasury and U.S. government agencies
Investment Holdings [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	4,993	11,625
Available for Sale, Less Than 12 Months, Unrealized Losses	2	39
Available for Sale, 12 Months or Longer, Fair Value	21,228	41,617
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 316	$ 397
Available for Sale, Number of Securities (in shares) \| security	7	11
Available for Sale, Total, Fair Value	$ 26,221	$ 53,242
Available for Sale, Total, Unrealized Losses	318	436
Held to Maturity, Less Than 12 Months, Fair Value		3,195
Held to Maturity, Less Than 12 Months, Unrealized Losses		6
Held to Maturity, 12 Months or Longer, Fair Value		5,102
Held to Maturity, 12 Months or Longer, Unrealized Losses		$ 2
Held to Maturity, Number of Securities (in shares) \| security		2
Held to Maturity, Total, Fair Value		$ 8,297
Held to Maturity, Total, Unrealized Losses		8
Mortgage-backed securities, residential
Investment Holdings [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	57,063	125,782
Available for Sale, Less Than 12 Months, Unrealized Losses	175	561
Available for Sale, 12 Months or Longer, Fair Value	6,021	99,489
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 71	$ 990
Available for Sale, Number of Securities (in shares) \| security	27	86
Available for Sale, Total, Fair Value	$ 63,084	$ 225,271
Available for Sale, Total, Unrealized Losses	246	1,551
Held to Maturity, Less Than 12 Months, Fair Value	119	12,462
Held to Maturity, Less Than 12 Months, Unrealized Losses	1	46
Held to Maturity, 12 Months or Longer, Fair Value	25	10,592
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 0	$ 130
Held to Maturity, Number of Securities (in shares) \| security	5	16
Held to Maturity, Total, Fair Value	$ 144	$ 23,054
Held to Maturity, Total, Unrealized Losses	1	176
Mortgage-backed securities, multifamily
Investment Holdings [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	2,557	7,651
Available for Sale, Less Than 12 Months, Unrealized Losses	13	118
Available for Sale, 12 Months or Longer, Fair Value	0	4,878
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 0	$ 5
Available for Sale, Number of Securities (in shares) \| security	2	3
Available for Sale, Total, Fair Value	$ 2,557	$ 12,529
Available for Sale, Total, Unrealized Losses	13	123
Held to Maturity, Less Than 12 Months, Fair Value		0
Held to Maturity, Less Than 12 Months, Unrealized Losses		0
Held to Maturity, 12 Months or Longer, Fair Value		998
Held to Maturity, 12 Months or Longer, Unrealized Losses		$ 2
Held to Maturity, Number of Securities (in shares) \| security		1
Held to Maturity, Total, Fair Value		$ 998
Held to Maturity, Total, Unrealized Losses		2
Asset-backed securities
Investment Holdings [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	40,711
Available for Sale, Less Than 12 Months, Unrealized Losses	643
Available for Sale, 12 Months or Longer, Fair Value	0
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 0
Available for Sale, Number of Securities (in shares) \| security	6
Available for Sale, Total, Fair Value	$ 40,711
Available for Sale, Total, Unrealized Losses	643
Obligations of states and political subdivisions
Investment Holdings [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	51,342	373
Available for Sale, Less Than 12 Months, Unrealized Losses	445	2
Available for Sale, 12 Months or Longer, Fair Value	0	6,559
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 0	$ 33
Available for Sale, Number of Securities (in shares) \| security	31	5
Available for Sale, Total, Fair Value	$ 51,342	$ 6,932
Available for Sale, Total, Unrealized Losses	445	$ 35
Debt securities
Investment Holdings [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	1,055
Available for Sale, Less Than 12 Months, Unrealized Losses	1
Available for Sale, 12 Months or Longer, Fair Value	0
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 0
Available for Sale, Number of Securities (in shares) \| security	1
Available for Sale, Total, Fair Value	$ 1,055
Available for Sale, Total, Unrealized Losses	$ 1

Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss

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Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value

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Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Number of Positions

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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