Fair Value Measurements and Available for Sale Investments (Tables)

9 Months Ended

Sep. 30, 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 September 30, 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 September 30, 2019
Money market funds		$	35,756	$	35,756	$	—	$	—
U.S. Treasury and agency securities			199,500		199,500		—		—
Commercial paper			30,985		—		30,985		—
Corporate debt securities			99,892		—		99,892		—
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 as of September 30, 2019 are as follows (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Total
	Cost		Gains		Losses			Fair Value
Marketable securities
U.S. Treasury and agency securities	$	185,844	$	145	$	(4	)	$	185,985
Commercial paper		29,887		—		—			29,887
Corporate debt securities		99,578		319		(5	)		99,892
Total marketable securities	$	315,309	$	464	$	(9	)	$	315,764

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

Contractual maturities of available-for-sale debt securities, as of September 30, 2019, were as follows (in thousands):

	Estimated
	Fair Value
Due within one year	$	290,813
One to two years		24,951
Total	$	315,764