Cash Equivalents and Investments in Marketable Securities - Unrealized Positions for Available-for-Sale Fixed-Maturity Debt Securities (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 21,696
Gross Unrealized Gains	0
Gross Unrealized Losses	(5)
Fair Value	21,691
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,830
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	4,830
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,497
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	1,497
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,994
Gross Unrealized Gains	0
Gross Unrealized Losses	(5)
Fair Value	6,989
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,375
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 8,375

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).

+ References

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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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