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Investments in Marketable Securities - Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Type of Security (Detail) - USD ($) $ in Thousands | Mar. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 188,069 | $ 209,985
Allowance for Credit Losses | 0 |
Fair Value | 189,074 | 211,561
Short-term investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 143,115 | 150,517
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 849 | 240
Gross Unrealized Losses | (100) | (5)
Fair Value | 143,864 | 150,752
Short-term investments [Member] | U.S. Treasuries [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 113,885 | 124,389
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 835 | 196
Gross Unrealized Losses | 0 | (5)
Fair Value | 114,720 | 124,580
Short-term investments [Member] | U.S. Government Sponsored Entities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 9,128 | 0
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 9 | 0
Gross Unrealized Losses | 0 | 0
Fair Value | 9,137 | 0
Short-term investments [Member] | Corporate debt [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 19,801 | 26,128
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 5 | 44
Gross Unrealized Losses | (95) | 0
Fair Value | 19,711 | 26,172
Short-term investments [Member] | ABS and other [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 301 |
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 0 |
Gross Unrealized Losses | (5) |
Fair Value | 296 |
Long-term marketable securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 44,954 | 59,468
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 1,202 | 1,358
Gross Unrealized Losses | (946) | (17)
Fair Value | 45,210 | 60,809
Long-term marketable securities [Member] | U.S. Treasuries [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 10,015 | 24,188
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 495 | 235
Gross Unrealized Losses | 0 | 0
Fair Value | 10,510 | 24,423
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 1,299 | 1,353
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 29 | 3
Gross Unrealized Losses | 0 | (1)
Fair Value | 1,328 | 1,355
Long-term marketable securities [Member] | Corporate debt [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 25,633 | 25,447
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 634 | 1,027
Gross Unrealized Losses | (661) | (3)
Fair Value | 25,606 | 26,471
Long-term marketable securities [Member] | ABS and other [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 8,007 | 8,480
Allowance for Credit Losses | 0 |
Gross Unrealized Gains | 44 | 93
Gross Unrealized Losses | (285) | (13)
Fair Value | $ 7,766 | $ 8,560

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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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