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Financial Instruments - Summary of Investments (Detail) - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
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Short-term, Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total short-term investments (available for sale), Cost | $ 1,538 | $ 1,361
Total short-term investments (available for sale), Gross Unrealized Gain | 2 | 3
Total short-term investments (available for sale), Fair value | 1,540 | 1,364
Short-term, Non-governmental Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total short-term investments (available for sale), Cost | 219,215 | 165,423
Total short-term investments (available for sale), Gross Unrealized Gain | 975 | 433
Total short-term investments (available for sale), Gross Unrealized (Loss) | (37) | (37)
Total short-term investments (available for sale), Fair value | 220,153 | 165,819
Short-term, Treasury and Federal Agencies [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total short-term investments (available for sale), Cost | 28,525 | 18,307
Total short-term investments (available for sale), Gross Unrealized Gain | 49 | 7
Total short-term investments (available for sale), Gross Unrealized (Loss) | (2) | (9)
Total short-term investments (available for sale), Fair value | 28,572 | 18,305
Short-term Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total short-term investments (available for sale), Cost | 249,278 | 185,091
Total short-term investments (available for sale), Gross Unrealized Gain | 1,026 | 443
Total short-term investments (available for sale), Gross Unrealized (Loss) | (39) | (46)
Total short-term investments (available for sale), Fair value | $ 250,265 | $ 185,488

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