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Marketable Securities (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Dec. 31, 2017
Schedule of Available-for-sale Securities |  |
Cash and cash equivalents | $ 34,996 | $ 16,528
Investments, amortized cost | 530,794 | 353,774
Investments | 528,465 | 351,975
Total amortized cost | 515,162 |
Gross unrealized gains | 1 |
Gross unrealized losses | (2,330) | (1,799)
Securities | 512,833 |
Marketable securities |  |
Schedule of Available-for-sale Securities |  |
Securities | 512,833 | 346,800
Money Market Funds |  |
Schedule of Available-for-sale Securities |  |
Cash and cash equivalents | 15,632 | 5,175
Corporate Securities |  |
Schedule of Available-for-sale Securities |  |
Total amortized cost | 98,498 | 123,860
Gross unrealized gains | 1 |
Gross unrealized losses | (471) | (590)
Securities | 98,028 | 123,270
Government Securities |  |
Schedule of Available-for-sale Securities |  |
Total amortized cost | 416,664 | 224,739
Gross unrealized losses | (1,859) | (1,209)
Securities | 414,805 | 223,530
Cash and Cash Equivalents |  |
Schedule of Available-for-sale Securities |  |
Cash and cash equivalents | $ 15,632 | $ 5,175

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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=82897076&loc=d3e27161-111563 + Details
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