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Investments - Cash Equivalents and Investments held at Fair Value (Detail) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | $ 46,147 | $ 45,116
Marketable equity securities | 800 | 800
Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Other investments | 1,400 | 1,400
Total | 84,344 | 82,217
Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Other investments | 1,400 | 1,400
Total | 47,966 | 46,976
Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total | 35,845 | 34,708
Fair Value, Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total | 533 | 533
Money Market Funds [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cash equivalents | 889 | 497
Money Market Funds [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cash equivalents | 889 | 497
Corporate Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 14,231 | 11,885
Corporate Bonds [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 14,231 | 11,885
Corporate Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 14,231 | 11,885
Municipal Fixed-Rate Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 2,625 | 2,884
Municipal Fixed-Rate Bonds [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 2,625 | 2,884
Municipal Fixed-Rate Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 2,625 | 2,884
Asset-Backed Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 5,812 | 6,708
Asset-Backed Bonds [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 5,812 | 6,708
Asset-Backed Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 5,812 | 6,708
Mortgage/Agency-Backed Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 11,845 | 11,644
Mortgage/Agency-Backed Bonds [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 11,845 | 11,644
Mortgage/Agency-Backed Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 11,845 | 11,644
U.S. Government Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 9,769 | 9,875
U.S. Government Bonds [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cash equivalents |  | 350
Available-for-sale debt securities | 9,769 | 9,875
U.S. Government Bonds [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Cash equivalents |  | 350
Available-for-sale debt securities | 9,769 | 9,875
Foreign Government Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 1,332 | 1,337
Foreign Government Bonds [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 1,332 | 1,337
Foreign Government Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 1,332 | 1,337
Commercial Paper [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities |  | 250
Commercial Paper [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities |  | 250
Commercial Paper [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities |  | 250
Other [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 533 | 533
Other [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 533 | 533
Other [Member] | Fair Value, Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale debt securities | 533 | 533
Marketable Equity Securities - Various Industries [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Marketable equity securities | 11,544 | 10,963
Marketable Equity Securities - Various Industries [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Marketable equity securities | 11,544 | 10,963
Deferred Compensation Plan Assets [Member] | Fair Value, Measurements [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Marketable equity securities | 24,364 | 23,891
Deferred Compensation Plan Assets [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Marketable equity securities | $ 24,364 | $ 23,891

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