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Investments - Contractual Maturities of Debt Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Fair Value/Carrying Value	$ 35,913	$ 40,799
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	3,154
One to two years	4,316
Two to three years	3,068
Three to five years	290
Available-for-sale debt securities, Fair Value/Carrying Value	10,828	20,684
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	930
Available-for-sale debt securities, Fair Value/Carrying Value	930	1,313
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	941
Two to three years	2,475
Three to five years	1,593
Five to ten years	1,666
More than ten years	580
Available-for-sale debt securities, Fair Value/Carrying Value	7,255	5,221
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	215
Two to three years	1,072
Three to five years	920
Five to ten years	680
More than ten years	4,501
Available-for-sale debt securities, Fair Value/Carrying Value	7,388	3,791
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Two to three years	7,528
Three to five years	1,615
Available-for-sale debt securities, Fair Value/Carrying Value	9,143	9,206
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Three to five years	369
Available-for-sale debt securities, Fair Value/Carrying Value	$ 369	$ 584

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