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Financial Instruments - Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | $ 185,488 | $ 196,428
Fair Value Measurements on Recurring Basis [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | 185,488 | 196,428
Fair Value Measurements on Recurring Basis [Member] | Municipal Bonds [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | 1,364 |
Fair Value Measurements on Recurring Basis [Member] | Non-governmental Debt Securities [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | 165,819 | 179,091
Fair Value Measurements on Recurring Basis [Member] | Treasury and Federal Agencies [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | 18,305 | 17,337
Fair Value Measurements on Recurring Basis [Member] | Level 1 [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value |  | 20,000
Fair Value Measurements on Recurring Basis [Member] | Level 1 [Member] | Non-governmental Debt Securities [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value |  | 20,000
Fair Value Measurements on Recurring Basis [Member] | Level 2 [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | 185,488 | 176,428
Fair Value Measurements on Recurring Basis [Member] | Level 2 [Member] | Municipal Bonds [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | 1,364 |
Fair Value Measurements on Recurring Basis [Member] | Level 2 [Member] | Non-governmental Debt Securities [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | 165,819 | 159,091
Fair Value Measurements on Recurring Basis [Member] | Level 2 [Member] | Treasury and Federal Agencies [Member] |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total investments at fair value | $ 18,305 | $ 17,337

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