Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Measurements

Summary of major categories of financial assets and financial liabilities measured at fair value on a recurring basis

	Level 1		Level 2		Level 3		Total
December 31, 2017
Assets
Money market funds (cash equivalents)	$	33,531	$	—	$	—	$	33,531
U.S. Treasury securities		—		24,825		—		24,825
Total assets	$	33,531	$	24,825	$	—	$	58,356
December 31, 2016
Assets
Money market funds (cash equivalents)	$	25,629	$	—	$	—	$	25,629
Certificates of deposit		3,922		—		—		3,922
Total assets	$	29,551	$	—	$	—	$	29,551