Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Summary of financial instruments measured at fair value on a recurring basis

The following table summarizes the financial instruments measured at fair value on a recurring basis in the accompanying condensed consolidated balance sheets as of June 30, 2018 and December 31, 2017 (in thousands):

	As of June 30, 2018
	Level 1		Level 2		Level 3		Total
Assets
Cash and cash equivalents:
Cash	$	19,018	$	—	$	—	$	19,018
Money market funds (1)	32,423		—		—		32,423
Total	$	51,441	$	—	$	—	$	51,441
Marketable Securities
Domestic corporate debt securities (2)	$	—	$	206,881	$	—	$	206,881
Agency bonds (2)	—		59,612		—		59,612
Total	$	—	$	266,493	$	—	$	266,493

	As of December 31, 2017
	Level 1		Level 2		Level 3		Total
Assets
Cash and cash equivalents:
Cash	$	73,302	$	—	$	—	$	73,302
Money market funds (1)	325		—		—		325
Domestic corporate commercial paper (2)	—		44,937		—		44,937
Total	$	73,627	$	44,937	$	—	$	118,564
Marketable Securities
Domestic corporate debt securities (2)	$	—	$	207,086	$	—	$	207,086
Domestic corporate commercial paper (2)	—		29,837		—		29,837
Agency bonds (2)	—		74,769		—		74,769
Total	$	—	$	311,692	$	—	$	311,692

(1) Fair value is based upon quoted market prices.

(2) Fair value is based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant assumptions are observable in the market or can be corroborated by observable market data for substantially the full term of the assets. Inputs are obtained from various sources, including market participants, dealers and brokers.