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Schedule of Available for Sale Marketable Securities (Detail) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
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Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | $ 487,503 | $ 259,011
Available-for-sale marketable securities, Unrealized Gain | 1,569 | 592
Available-for-sale marketable securities, Unrealized (Loss) | (1,347) | (2,967)
Available-for-sale marketable securities, Fair Market Value | 487,725 | 256,636
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | 120,039 | 191,978
U.S. Treasury Securities |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 191,715 | 110,969
Available-for-sale marketable securities, Unrealized Gain | 144 | 112
Available-for-sale marketable securities, Unrealized (Loss) | (816) | (1,360)
Available-for-sale marketable securities, Fair Market Value | 191,043 | 109,721
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | 82,132 | 75,040
Commercial Paper |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 180,610 | 86,130
Available-for-sale marketable securities, Unrealized Gain | 1 | 13
Available-for-sale marketable securities, Unrealized (Loss) | (7) | (26)
Available-for-sale marketable securities, Fair Market Value | 180,604 | 86,117
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | 11,237 | 85,094
Corporate Debt Securities |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 90,402 | 41,133
Available-for-sale marketable securities, Unrealized Gain | 1,343 | 432
Available-for-sale marketable securities, Unrealized (Loss) | (501) | (1,545)
Available-for-sale marketable securities, Fair Market Value | 91,244 | 40,020
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | 18,150 | 24,767
Certificates of Deposit and Time Deposits |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 11,497 | 7,604
Available-for-sale marketable securities, Unrealized Gain | 1 |
Available-for-sale marketable securities, Unrealized (Loss) | (2) |
Available-for-sale marketable securities, Fair Market Value | 11,496 | 7,604
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | 4,419 |
U.S. Government Agency Securities |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 9,646 | 9,646
Available-for-sale marketable securities, Unrealized Gain | 4 | 1
Available-for-sale marketable securities, Unrealized (Loss) | (21) | (36)
Available-for-sale marketable securities, Fair Market Value | 9,629 | 9,611
Available-for-sale marketable securities, Fair Market Value of Investments with Unrealized Losses | 4,101 | 7,077
Debt Mutual Funds |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 3,255 | 3,153
Available-for-sale marketable securities, Unrealized Gain | 76 | 34
Available-for-sale marketable securities, Fair Market Value | 3,331 | 3,187
Non-U.S. Government Securities |  |
Schedule of Available-for-sale Securities |  |
Available-for-sale marketable securities, Cost | 378 | 376
Available-for-sale marketable securities, Fair Market Value | $ 378 | $ 376

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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as 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=82897076&loc=d3e27161-111563 + Details
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