Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following tables summarize our financial assets and liabilities measured at fair value on a recurring basis (in thousands):

	December 31, 2017
	LEVEL 1		LEVEL 2		LEVEL 3		TOTAL
Assets:
Money market funds	$	70,502	$	—	$	—	$	70,502
U.S. Treasury securities	68,653		—		—		68,653
Total	$	139,155	$	—	$	—	$	139,155

	December 31, 2016
	LEVEL 1		LEVEL 2		LEVEL 3		TOTAL
Assets:
Money market funds	$	36,414	$	—	$	—	$	36,414
U.S. Treasury securities	62,040		—		—		$	62,040
Total	$	98,454	$	—	$	—	$	98,454