Investment Securities - Gross Unrealized Losses and Fair Value, Aggregated by Investment Category (Detail) $ in Thousands	Sep. 30, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	$ 487,009
Less than 12 Months, Unrealized Losses	(4,569)
12 Months or More, Fair Value	1,957
12 Months or More, Unrealized Losses	(43)
Fair Value, Total	488,966
Unrealized Losses	(4,612)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	21,800
Less than 12 Months, Unrealized Losses	(125)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	21,800
Unrealized Losses	(125)
Agency-guaranteed residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	9,666
Less than 12 Months, Unrealized Losses	(258)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	9,666
Unrealized Losses	(258)
Agency-guaranteed commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	0
Less than 12 Months, Unrealized Losses	0
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	0
Unrealized Losses	0
Agency-guaranteed residential collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	25,548
Less than 12 Months, Unrealized Losses	(90)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	25,548
Unrealized Losses	(90)
Agency-guaranteed commercial collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	121,156
Less than 12 Months, Unrealized Losses	(2,106)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	121,156
Unrealized Losses	(2,106)
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	71,508
Less than 12 Months, Unrealized Losses	(109)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	71,508
Unrealized Losses	(109)
Corporate notes
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	98,662
Less than 12 Months, Unrealized Losses	(504)
12 Months or More, Fair Value	1,957
12 Months or More, Unrealized Losses	(43)
Fair Value, Total	100,619
Unrealized Losses	(547)
Private label collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	138,669
Less than 12 Months, Unrealized Losses	(1,377)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	138,669
Unrealized Losses	$ (1,377)

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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