Investment Securities (Securities Held to Maturity by Contractual Maturity) (Detail) $ in Thousands	Mar. 31, 2021 USD ($)
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, amortized cost	$ 0
Due after one year through five years, amortized cost	163,682
Due after five years through ten years, amortized cost	213,875
Due after ten years, amortized cost	70,372
Amortized cost	447,929
Due in one year or less, fair value	0
Due after one year through five years, fair value	167,460
Due after five years through ten years, fair value	224,327
Due after ten years, fair value	72,155
Fair value	$ 463,942

Fair value of investment in debt security measured at amortized cost (held-to-maturity), 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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Fair value of investment in debt security measured at amortized cost (held-to-maturity), 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 amortized cost (held-to-maturity), with single maturity date and allocated without single maturity date, maturing after 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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Fair value of investment in debt security measured at amortized cost (held-to-maturity), 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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