Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Measurements [Abstract]

Fair Value, Marketable Securities Measured on Recurring and Nonrecurring Basis

Financial assets carried at fair value are classified in the tables below in one of the three categories described above:

			Fair Value Measurements Using
	Total		Level 1		Level 2		Level 3
	(in thousands)
March 31, 2020
Assets
Cash and cash equivalents:
Money market funds	$	24,773	$	24,773	$	—	$	—
Available-for-sale investment debt securities:
Commercial paper		18,488		—		18,488		—
Corporate debt securities		485,098		—		485,098		—
U.S. treasuries		4,042		—		4,042		—
Total financial assets	$	532,401	$	24,773	$	507,628	$	—
December 31, 2019
Assets
Cash and cash equivalents:
Money market funds	$	19,376	$	19,376	$	—	$	—
Commercial paper		7,498		—		7,498		—
Available-for-sale investment debt securities:
Commercial paper		42,848		—		42,848		—
Corporate debt securities		539,719		—		539,719		—
Total financial assets	$	609,441	$	19,376	$	590,065	$	—

Schedule of Available for Sale Securities Debt Maturities

The aggregate fair value of all available-for-sale investment debt securities (commercial paper, corporate debt securities and U.S. treasuries), by contractual maturity, are as follows:

	Fair Value as of
	March 31, 2020		December 31, 2019
	(in thousands)
Due in one year or less	$	433,013	$	473,602
Due after one year through two years		74,615		116,463
Total investment debt securities	$	507,628	$	590,065