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Investments - Contractual Maturities of Debt Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Fair Value/Carrying Value	$ 40,799	$ 62,493
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	2,127
One to two years	11,557
Two to three years	6,831
Three to five years	169
Available-for-sale debt securities, Fair Value/Carrying Value	20,684	32,543
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	176
One to two years	208
Two to three years	929
Available-for-sale debt securities, Fair Value/Carrying Value	1,313	2,882
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	943
One to two years	401
Two to three years	193
Three to five years	2,433
Five to ten years	260
More than ten years	991
Available-for-sale debt securities, Fair Value/Carrying Value	5,221	6,526
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Two to three years	425
Three to five years	853
Five to ten years	6
More than ten years	2,507
Available-for-sale debt securities, Fair Value/Carrying Value	3,791	5,509
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	6,714
Three to five years	2,492
Available-for-sale debt securities, Fair Value/Carrying Value	9,206	14,303
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	285
Two to three years	299
Available-for-sale debt securities, Fair Value/Carrying Value	$ 584	$ 730

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