Investment Securities Held-to-Maturity - Company's Securities Held-to-Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 73,576
After one but within five years, Amortized Cost	1,891,043
After five but within ten years, Amortized Cost	374,071
More than ten years, Amortized Cost	12,430
Amortized Cost	2,351,120	$ 2,046,647
Within one year, Fair Value	73,841
After one but within five years, Fair Value	1,900,050
After five but within ten years, Fair Value	374,688
More than ten years, Fair Value	12,725
Estimated Fair Value	$ 2,361,304	$ 1,991,421

Amount of investment in debt security measured at amortized cost (held-to-maturity).

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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 sixth through tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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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 through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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