Investment Securities - Maturity of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Net Investment Income [Line Items]
Due within one year, Amortized Cost	$ 4,998
Due within one year, Estimated Fair Value	5,053
Due after one but within five years, Amortized Cost	8,878
Due after one but within five years, Estimated Fair Value	8,915
Due after five but within ten years, Amortized Cost	28,707
Due after five but within ten years, Estimated Fair Value	27,683
Due after ten years, Amortized Cost	0
Due after ten years, Estimated Fair Value	0
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	42,583
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	41,651
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	952,074
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	891,553
Amortized Cost	994,657	$ 1,045,579
Securities available for sale, at fair value	933,204	$ 1,041,380
Debt Securities [Member]
Net Investment Income [Line Items]
Amortized Cost	994,657
Securities available for sale, at fair value	933,204
US Government Agencies Debt Securities [Member]
Net Investment Income [Line Items]
Amortized Cost	355,800
Securities available for sale, at fair value	334,300
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Net Investment Income [Line Items]
Amortized Cost	596,300
Securities available for sale, at fair value	$ 557,300

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), without single maturity date and not allocated over maturity grouping.

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), without single maturity date and not allocated over maturity grouping.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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