Investment Securities - Gross Unrealized Losses and Fair Value, Aggregated by Investment Category (Detail) $ in Thousands	Mar. 31, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	$ 369,291
Less than 12 Months, Unrealized Losses	(3,666)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	369,291
Unrealized Losses	(3,666)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	90,064
Less than 12 Months, Unrealized Losses	(249)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	90,064
Unrealized Losses	(249)
Agency-guaranteed residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	10,377
Less than 12 Months, Unrealized Losses	(308)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	10,377
Unrealized Losses	(308)
Agency-guaranteed collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	55,825
Less than 12 Months, Unrealized Losses	(487)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	55,825
Unrealized Losses	(487)
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	55,703
Less than 12 Months, Unrealized Losses	(43)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	55,703
Unrealized Losses	(43)
Corporate notes
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	48,905
Less than 12 Months, Unrealized Losses	(624)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	48,905
Unrealized Losses	(624)
Private label collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months, Fair Value	108,417
Less than 12 Months, Unrealized Losses	(1,955)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Fair Value, Total	108,417
Unrealized Losses	$ (1,955)

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 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 less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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