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Financial Instruments - Summary of Investments (Detail) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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Schedule of Available-for-sale Securities [Line Items] |  |
Total short-term investments (available for sale), Fair value | $ 185,488 | $ 196,428
Short-term, Municipal Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total short-term investments (available for sale), Cost | 1,361 |
Total short-term investments (available for sale), Gross Unrealized Gain | 3 |
Total short-term investments (available for sale), Fair value | 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 | 165,423 | 179,393
Total short-term investments (available for sale), Gross Unrealized Gain | 433 | 35
Total short-term investments (available for sale), Gross Unrealized (Loss) | (37) | (337)
Total short-term investments (available for sale), Fair value | 165,819 | 179,091
Short-term, Treasury and Federal Agencies [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total short-term investments (available for sale), Cost | 18,307 | 17,417
Total short-term investments (available for sale), Gross Unrealized Gain | 7 | 5
Total short-term investments (available for sale), Gross Unrealized (Loss) | (9) | (85)
Total short-term investments (available for sale), Fair value | 18,305 | 17,337
Short-term Investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Total short-term investments (available for sale), Cost | 185,091 | 196,810
Total short-term investments (available for sale), Gross Unrealized Gain | 443 | 40
Total short-term investments (available for sale), Gross Unrealized (Loss) | (46) | (422)
Total short-term investments (available for sale), Fair value | $ 185,488 | $ 196,428

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
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