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Investments - Contractual Maturities of Debt Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Fair Value/Carrying Value	$ 45,116	$ 37,700	$ 37,660
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	1,477
One to two years	2,007
Two to three years	7,013
Three to five years	1,388
Available-for-sale debt securities, Fair Value/Carrying Value	11,885		9,384
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	96
One to two years	1,245
Two to three years	1,246
Three to five years	297
Available-for-sale debt securities, Fair Value/Carrying Value	2,884		930
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	144
One to two years	300
Two to three years	622
Three to five years	3,658
Five to ten years	1,241
More than ten years	743
Available-for-sale debt securities, Fair Value/Carrying Value	6,708		6,890
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	63
One to two years	2,129
Two to three years	2,940
Three to five years	183
Five to ten years	2,095
More than ten years	4,234
Available-for-sale debt securities, Fair Value/Carrying Value	11,644		6,962
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	5,122
Two to three years	4,526
Three to five years	227
Available-for-sale debt securities, Fair Value/Carrying Value	9,875		12,323
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	75
One to two years	462
Two to three years	498
Three to five years	302
Available-for-sale debt securities, Fair Value/Carrying Value	1,337		$ 371
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	250
Available-for-sale debt securities, Fair Value/Carrying Value	250
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	533
Available-for-sale debt securities, Fair Value/Carrying Value	$ 533

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