Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Summary of financial assets and liabilities 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 consolidated balance sheets as of December 31, 2017 and December 31, 2016 (in thousands):



	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
Asset-backed securities (2)	—		74,769		—		74,769
Total	$	—	$	311,692	$	—	$	311,692



	As of December 31, 2016
	Level 1		Level 2		Level 3		Total
Assets
Cash and cash equivalents:
Cash	$	77,443	$	—	$	—	$	77,443
Money market funds (1)	173,631		—		—		173,631
Domestic corporate commercial paper (2)	—		5,487		—		5,487
Domestic corporate debt securities (2)	—		2,006		—		2,006
Total	$	251,074	$	7,493	$	—	$	258,567
Marketable securities:
Domestic corporate debt securities (2)	$	—	$	19,315	$	—	$	19,315
Domestic corporate commercial paper (2)	—		31,930		—		31,930
Asset-backed securities (2)	—		22,635		—		22,635
Total	$	—	$	73,880	$	—	$	73,880

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(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.