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Investments - Contractual Maturities of Debt Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Fair Value/Carrying Value	$ 34,033	$ 40,799
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	2,749
One to two years	8,460
Two to three years	3,030
Available-for-sale debt securities, Fair Value/Carrying Value	14,239	20,684
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	927
Available-for-sale debt securities, Fair Value/Carrying Value	927	1,313
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	96
One to two years	430
Two to three years	1,667
Three to five years	2,018
Five to ten years	1,772
More than ten years	626
Available-for-sale debt securities, Fair Value/Carrying Value	6,609	5,221
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	264
Two to three years	588
Three to five years	510
Five to ten years	425
More than ten years	3,592
Available-for-sale debt securities, Fair Value/Carrying Value	5,379	3,791
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	2,443
Two to three years	1,346
Three to five years	1,238
Available-for-sale debt securities, Fair Value/Carrying Value	5,027	9,206
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	891
Two to three years	961
Available-for-sale debt securities, Fair Value/Carrying Value	$ 1,852	$ 584

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