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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, 2021 | Dec. 31, 2020
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 199,574 | $ 203,329
Allowance for Credit Losses | 0 |
Fair Value | 201,425 | 206,031
Short-term investments [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 134,460 | 158,148
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 34 | 116
Gross Unrealized Losses | 0 | (6)
Fair Value | 134,494 | 158,258
Short-term investments [Member] | U.S. Treasuries [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 69,217 | 75,887
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 23 | 88
Gross Unrealized Losses | 0 | (5)
Fair Value | 69,240 | 75,970
Short-term investments [Member] | U.S. Government Sponsored Entities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 11,450 | 32,439
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 4 | 8
Gross Unrealized Losses | 0 | 0
Fair Value | 11,454 | 32,447
Short-term investments [Member] | Corporate debt [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 53,793 | 49,822
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 7 | 20
Gross Unrealized Losses | 0 | (1)
Fair Value | 53,800 | 49,841
Long-term marketable securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 65,114 | 45,181
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 1,886 | 2,636
Gross Unrealized Losses | (69) | (44)
Fair Value | 66,931 | 47,773
Long-term marketable securities [Member] | U.S. Treasuries [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 22,342 | 3,375
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 179 | 266
Gross Unrealized Losses | 0 | 0
Fair Value | 22,521 | 3,641
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 1,012 | 1,114
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 36 | 38
Gross Unrealized Losses | (3) | 0
Fair Value | 1,045 | 1,152
Long-term marketable securities [Member] | Corporate debt [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 35,424 | 34,183
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 1,505 | 2,137
Gross Unrealized Losses | (60) | (33)
Fair Value | 36,869 | 36,287
Long-term marketable securities [Member] | Asset-backed Securities ("ABS") and Other [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 6,336 | 6,509
Allowance for Credit Losses | 0 | 0
Gross Unrealized Gains | 166 | 195
Gross Unrealized Losses | (6) | (11)
Fair Value | $ 6,496 | $ 6,693

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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=121645371&loc=d3e27161-111563 + Details
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