Investment Securities - Gross Unrealized Losses on Debt Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available for Sale, Less than 12 Months, Fair Value	$ 693,862	$ 212,087
Debt Securities, Available for Sale, Less than 12 Months, Unrealized Loss	(5,400)	(1,332)
Debt Securities, Available for Sale, 12 Months or more, Fair Value	152,895	297,020
Debt Securities, Available for Sale, 12 Months or more, Unrealized Loss	(1,222)	(4,710)
Debt Securities, Available for Sale, Fair Value	846,757	509,107
Debt Securities, Available-for-sale, Unrealized Loss	(6,622)	(6,042)
Obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available for Sale, Less than 12 Months, Fair Value	566,137	160,543
Debt Securities, Available for Sale, Less than 12 Months, Unrealized Loss	(4,554)	(891)
Debt Securities, Available for Sale, 12 Months or more, Fair Value	0	0
Debt Securities, Available for Sale, 12 Months or more, Unrealized Loss	0	0
Debt Securities, Available for Sale, Fair Value	566,137	160,543
Debt Securities, Available-for-sale, Unrealized Loss	(4,554)	(891)
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available for Sale, Less than 12 Months, Fair Value	24,207
Debt Securities, Available for Sale, Less than 12 Months, Unrealized Loss	(452)
Debt Securities, Available for Sale, 12 Months or more, Fair Value	0
Debt Securities, Available for Sale, 12 Months or more, Unrealized Loss	0
Debt Securities, Available for Sale, Fair Value	24,207
Debt Securities, Available-for-sale, Unrealized Loss	(452)
Asset backed securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available for Sale, Less than 12 Months, Fair Value	103,518	51,544
Debt Securities, Available for Sale, Less than 12 Months, Unrealized Loss	(394)	(441)
Debt Securities, Available for Sale, 12 Months or more, Fair Value	152,895	297,020
Debt Securities, Available for Sale, 12 Months or more, Unrealized Loss	(1,222)	(4,710)
Debt Securities, Available for Sale, Fair Value	256,413	348,564
Debt Securities, Available-for-sale, Unrealized Loss	$ (1,616)	$ (5,151)

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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