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Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities
Cash and cash equivalents	$ 26,246	$ 16,528
Investments, amortized cost	523,454	353,774
Investments	522,493	351,975
Total amortized cost	505,184
Gross unrealized gains	188
Gross unrealized losses	(1,149)	(1,799)
Securities	504,223
Marketable securities
Schedule of Available-for-sale Securities
Securities	504,223	346,800
Money Market Funds
Schedule of Available-for-sale Securities
Cash and cash equivalents	18,270	5,175
Corporate Securities
Schedule of Available-for-sale Securities
Total amortized cost	105,311	123,860
Gross unrealized gains	1
Gross unrealized losses	(345)	(590)
Securities	104,967	123,270
Government Securities
Schedule of Available-for-sale Securities
Total amortized cost	399,873	224,739
Gross unrealized gains	187
Gross unrealized losses	(804)	(1,209)
Securities	399,256	223,530
Cash and Cash Equivalents
Schedule of Available-for-sale Securities
Cash and cash equivalents	$ 18,270	$ 5,175

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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).

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