Fair Value Measurements and Available for Sale Investments (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Measurements And Available For Sale Investments [Abstract]

Assets Measured at Fair Value on Recurring Basis

The following table presents the hierarchy for assets measured at fair value on a recurring basis as of March 31, 2019 and December 31, 2018 (in thousands):

	Fair Value Measurements at End of Period Using:
				Quoted Market		Significant		Significant
				Prices for		Other Observable		Unobservable
		Total		Identical Assets		Inputs		Inputs
		Fair Value		(Level 1)		(Level 2)		(Level 3)
As of March 31, 2019
Money market funds		$	40,965	$	40,965	$	—	$	—
U.S. Treasury securities			199,874		199,874		—		—
Commercial paper			26,687		—		26,687		—
Corporate debt securities			83,813		—		83,813		—
As of December 31, 2018
Money market funds		$	17,295	$	17,295	$	—	$	—
U.S. Treasury securities			123,439		123,439		—		—

Schedule of Available for Sale Investments by Security Type

The aggregate market value, cost basis, and gross unrealized gains and losses of available-for-sale investments by security type, classified in marketable securities and long-term investments for the three months ended March 31, 2019 are as follows (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Total
	Cost		Gains		Losses			Fair Value
Marketable securities
U.S. Treasury securities	$	199,811	$	69	$	(6	)	$	199,874
Commercial paper		26,694		—		(7	)		26,687
Corporate debt securities		83,738		84		(9	)		83,813
Total marketable securities	$	310,243	$	153	$	(22	)	$	310,374

Schedule of Contractual Maturities of Available-for-sale Debt Securities

Contractual maturities of available-for-sale debt securities, as of March 31, 2019, were as follows (in thousands):

	Estimated
	Fair Value
Due within one year	$	261,450
One to two years		48,924
Total	$	310,374