Marketable Securities - Schedule of Available-for-sale Marketable Securities and Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Cash and cash equivalents:
Cash and cash equivalents, Amortized Cost Value	$ 71,504	$ 59,321
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	71,504	59,321
Marketable securities:
Marketable securities, Amortized Cost Value	132,960	177,895
Marketable securities, Gross Unrealized Gains	0	0
Marketable securities, Gross Unrealized Losses	(281)	(755)
Marketable Securities	132,679	177,140
Domestic corporate debt securities
Marketable securities:
Marketable securities, Amortized Cost Value	87,940	132,886
Marketable securities, Gross Unrealized Gains	0	0
Marketable securities, Gross Unrealized Losses	(180)	(530)
Marketable Securities	87,760	132,356
Agency bonds
Marketable securities:
Marketable securities, Amortized Cost Value	45,020	45,009
Marketable securities, Gross Unrealized Gains	0	0
Marketable securities, Gross Unrealized Losses	(101)	(225)
Marketable Securities	44,919	44,784
Cash
Cash and cash equivalents:
Cash and cash equivalents, Amortized Cost Value	60,535	20,448
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	60,535	20,448
Money market funds
Cash and cash equivalents:
Cash and cash equivalents, Amortized Cost Value	10,969	38,873
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Fair Value	$ 10,969	$ 38,873

Cash And Cash Equivalents, Accumulated Gross Unrealized Gain, Before Tax

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Cash And Cash Equivalents, Accumulated Gross Unrealized Loss, Before Tax

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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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Amount, before tax, of unrealized loss 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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Amortized cost of 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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Amount of 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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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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