Investments - Investment Securities Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Less Than 12 Months		$ 21,074
Held-to-Maturity, Gross Unrealized Losses, Less Than 12 Months		193
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, 12 Months or Greater		3,311
Held-to-Maturity, Gross Unrealized Losses, 12 Months or Greater		13
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total		24,385
Held-to-Maturity, Gross Unrealized Losses, Total		206
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	$ 4,648	23,573
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	5	122
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater		18,220
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater		43
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	4,648	41,793
Available-for Sale, Gross Unrealized Losses, Total	5	165
Fair Value of Investments with Unrealized Losses, Less Than 12 months		44,647
Gross Unrealized Loss, Less Than 12 Months		315
Fair Value of Investments with Unrealized Losses, 12 Months or Greater		21,531
Gross Unrealized Losses, 12 Months or Greater		56
Fair Value of Investments with Unrealized Losses, Total		66,178
Gross Unrealized Losses, Total		371
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	2,515	6,426
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	3	1
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	2,515	6,426
Available-for Sale, Gross Unrealized Losses, Total	3	1
U.S. Agency-Based Mortgage-Backed Securities [Member]
Marketable Securities [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	2,133	13,007
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	2	95
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater		1,152
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater		1
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	2,133	14,159
Available-for Sale, Gross Unrealized Losses, Total	$ 2	96
States and Political Subdivisions [Member]
Marketable Securities [Line Items]
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Less Than 12 Months		21,074
Held-to-Maturity, Gross Unrealized Losses, Less Than 12 Months		193
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total		21,074
Held-to-Maturity, Gross Unrealized Losses, Total		193
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months		4,140
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months		26
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total		4,140
Available-for Sale, Gross Unrealized Losses, Total		26
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Marketable Securities [Line Items]
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, 12 Months or Greater		3,243
Held-to-Maturity, Gross Unrealized Losses, 12 Months or Greater		12
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total		3,243
Held-to-Maturity, Gross Unrealized Losses, Total		12
Available-for Sale, Fair Value of Investments with Unrealized Losses, 12 Months or Greater		17,068
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater		42
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total		17,068
Available-for Sale, Gross Unrealized Losses, Total		42
Asset-Backed Securities [Member]
Marketable Securities [Line Items]
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, 12 Months or Greater		68
Held-to-Maturity, Gross Unrealized Losses, 12 Months or Greater		1
Held-to-Maturity, Fair Value of Investments with Unrealized Losses, Total		68
Held-to-Maturity, Gross Unrealized Losses, Total		$ 1

Continuous unrealized loss position greater than twelve months aggregate losses.

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Continuous unrealized loss position greater than twelve months fair value.

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Continuous unrealized loss position less than twelve months aggregate losses.

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Securities continuous unrealized loss position aggregate losses.

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Securities continuous unrealized loss position fair value.

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

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Amount of accumulated unrealized loss on 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 12 months or longer, 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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Amount of accumulated unrealized loss on 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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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months.

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